I would say
Disneyland as part of a Southern California Vacation. There is so much to do that without knowing what else your family is into all I am going to say is click google maps on another tab or window on your computer and move around to the LA area and then use the + to zoom in and move around. There is everything from nature places and state parks, to several museums. Personally I would spend 3 days in the N LA area at least N of I-10 which is right in the downtown area, and S of I-210 then I would either drive or see if I could take a train to the San Diego area for 3days going to the Sab Diego Zoo and Sea World and I would finish off staying close to Disneyland.
So a 14 day trip would look something like this.
Day 1 Fly into LA
Day 2 N LA area
Day 3 N LA area
Day 4 N LA area
Day 5 Travel to San Diego
Day 6 San Diego
Day 7 San Diego
Day 8 San Diego
Day 9 Travel to Aniheim Area
Day 10 Disneyland
Day 11 Disneyland
Day 12 Disneyland
Day 13 Disneyland
Day 14 Time to get on the plane and head home it was a great vacation.
If you wanted to have 5 days at Disneyland I would change travel to San Diego on day 4.
When my siblings and I were close to the ages of your older 2 (We were 14, 12, and 11) my parents took us on a trip to the LA area and this is what we did and the general reactions.
Long Beach actually on the beach at night. This was fun even if we were not able to go much in the water due to it being dark (A great Uncle took us and our parents after we had dinner at his house with him and great aunt who served us what we thought were black eyed peas but no they just had half a container of pepper all over them).
Queen Mary and Spruce Goose boring as all get out
Universal the backlot tour which was the only attraction at the time was interesting though I was disappointed because I wanted a part when they asked for audience volunteers because at the time I really wanted to go into acting and not only did I not get one my younger brother did. And then he went on about why did they have to pick him he didn't even raise his hand when they asked.
Newport Beach loved it, really nice sand spent a whole day here and since it was in December practically had it to ourselves, we packed a lunch for the day.
Disneyland for one whole day from rope drop to the kiss goodnight 2 days before Christmas loved it wish we could have said longer-this was in the mid 80s so only one park. Favorite foods were a toss up between churos and pineapple spears. Years later we would not only get a costco but a resturant chain called Taco Johns that both serve good churos even if they are smaller at least it's somthing. The pineapple spears well for those we are on our own and have to cut a pineapple.
Magic Mountain fun riding the coasters if your a thrill seeker I am not so I watched a few of the shows and rode the carosaul a lot and did some of the tamer rides. It is under different managment than it was a that time. When we went it was a six flags park but it is no longer and from what I have heard from people who went to it both in the mid 80s and early 00s it has changed drastically and not necessarily for the better. It is still a good park if you are into coasters from what I have heard from but they have cut out a lot of the tamer stuff that is not geared for those not big enough to ride the coasters and a lot of the shows the used to have are no longer there and no other shows have replaced them.
Driving around Hollywood and Beverly Hills was a lot of fun though lots of people and traffic. Loved the holiday light displays in Beverly Hills when my grandmother's much younger cousin (like close in age to my mom younger) husband took us around after dinner which did not include black pepper peas and showed us the lights and even pointed out the houses of some of their celebrity clients as professional massage therapists. Coming from an area where at the time with a few execeptions if you went all out on holiday decorating you hung a row of lights along the edge of your roof where it attached to your house in addition to outlining the biggest window on the front of your house it was fun seeing not only the entire house outlined in lights but decorations in the yards and some of them even had music playing if you rolled down your window.
Sea World shows were fun at the time there were no rides it was just shows and getting to pet the dolphins which you could do for free and feed them which did cost and my parents said no to us doing that. My brother did not like it well he liked the shows he didn't like the sea gulls and would have declared open season on them because they kept going on him and I will leave the rest of that to your imagination. We drove there and back from where were were staying in Santa Monica in a very long day made even longer by what we thought was a random dui check but found out later that they were actually searching for drugs smuggled into the country from the southern boarder and some of the drug cartels. As we approached the inspection area my parents gave us very specific instructions not to be a bunch of smart rear ends and to only speak to answer a direction question otherwise they would do all the talking even though we did not have anything we should not have had. I think when my parents answered where are you coming from and where are you going with we are coming from spending the day at Sea World and we are going to relatives apartment in Santa Monica that is a college student but is actually in our hometown visiting family and is letting us stay there us kids might have been asked something like did you like Sea World or what was your favorite show but other than that us kids had no interaction. I think they might have also asked me being 14 if I had any identification and I might have showed them my really bad photo school id card.
Driving around San Fransisco and going to Fishermans Warf we found interesting though we could not figure out why people would want to litter and toss paper out the windows onto the street. This was on NYE and everyone was tossing their old single page date calendars. It was interesting driving too since as a lot of cars back then we had a manual transmission. My dad who was not only used to 3 on the tree or 4 on the floor but 8 and even larger stick shift systems (the 8 were 2 ton farm trucks he had been driving since big enough to reach the pedals and see over the dash and yes that was before it was legal for him to do so) said that he would never again drive the streets of San Fransisco in a stick and next time he was making sure he had an automatic. (San Fransisco is also a couple of days drive or a long 2 days we actually went from another relative's house in Ventura County which is about an hour or so N of the LA area to near San Jose where we stayed at yet another relative's house and then to San Fransisco where we spent most of the day and onto Sacramento area where we stayed with a family friend at their house. What was supposed to be 15 days away but turned into 16 because my parents decided they did not want to hit a certain spot where if we ended up having to stay because the roads were shut down with the blizzard that was supposed to hit about the time we got to the general area in the wee hours of the morning and there were not a lot of rooms in that area so we stopped in an area where they knew we could get a place to stay the night and that was the only night on the entire trip we stayed in a motel otherwise it was relative's houses or sleeping in the car as my parents took turns driving straight through and we took turns staying awake and talking with the driver).