You are doing the opposite of us, we are DL veterans headed to WDW for the first time on April 1!! AND you are the same, we are me, dh and 12 yo ds!!!!!
We have been to DL during busy times and slow times. 3 days is good, 4 is better. It will be busy that week, so make some plans and make sure you enjoy the pool! The parks have extended hours that entire week, DL until midnight, DCA until 10pm. DL and DCA are so much smaller that what you are used to. You will not have to board a bus at all! Make sure you get hopper passes to go back and forth between DL and DCA. You should have nice weather, last time I was there in April it was warm during day, sweatshirt at night.
There are a number of attractions that are unique to DL/DCA that you must do including Matterhorn, Indiana Jones, Roger Rabbit CarToon Spin, California Screamin are some of the best, plus Pirates is much better I have heard and Haunted Mansion is different as well.
Make sure you see Disney's Electrical Parade at DCA, looks like it is at 8:45 pm that week. Also there will be fireworks each night, so you can see them from inside the park, outside the park, and from different vantage points. Also you can be on attractions while everyone else is watching the fireworks.
Places your 12 yo would like to eat (I have a 12 yo ds too)
Blue Bayou (get reservations), it is right in the Pirates of Caribbean ride
Redd Rockets Pizza Port in Tomorrowland, a great counter service place
Pizza Oom Mow Mow in DCA
Rainforest Cafe in Downtown Disney (also get reservations)
ESPN Zone in Downtown Disney, great food, plus huge arcade
I have heard great things about Napa Rose at GCH, and IF your ds wants to do a character meal, the Storyteller's place at your hotel is great food and has I think Chip and Dale. We have never been either place. We also liked Ralph Brennans Jazz Kitchen in DTD, great food and atmosphere
Visit Downtown Disney there is a great
Lego store, again, 12 yo love that! Also the World of Disney is there. There are other shops, and movie theaters.
If you have a car, you may want to take part of a day and drive down to Huntington Beach, should take about 45 minutes. The beach is great, lots of surfers to watch, and there is a pier out into the ocean with a great kite store. Surf shops and places to eat are all over. I would take the time if you can, just to see the ocean. As for other attractions, most are at least an hour plus away. You may want to visit the Aquarium in Long Beach, probably the closest. My mom says it is a great place!
Well hope this helps. Ask more questions if you need to. Have a great time!