Here are some things we did with our daughter.
First to get her geared up to be with the characters we watched her Disney World Beach Party Video and
Disneyland Fun Videos that feature the characters throughout. Doing this made her excited and used to seeing the characters instead of afraid and shying back. Did this consistently for two weeks before we went. Not sure how old your toddlers are so it might not apply.
Some things our daughter loved were:
Small World
Peter Pan's Flight
Dumbo
Cinderella's Carousel
Winnie the Pooh
She loved Buzz Lightyear in Tomorrowland as well.
She loved the Parades!
Try to get to the rope drop for Mickey's Toon Town Fair.. We did that and headed straight for Mickey's House and were one of the first to get to see Mickey that day. Was great because they don't really rush you through so you get to actually stay with Mickey for a minute or two.. She loved that.
She loved digging for fossils in the Dinosaur Exhibit in Animal Kingdom and doing all sorts of exploring.
MGM she loved the Playhouse Disney show they had with Bear in the Big Blue House. If your toddlers love Playhouse Disney then this is a do not miss!
She also enjoyed the atmosphere at 50's Primetime Cafe in MGM. Uncle Dave our waiter just loved her and really made a big scene over her. She loved the dessert menu being on a view master. Fun place overall for kids..
If your daughter loves princesses try to get into Cinderella's Breakfast. Our DD got to meet Cinderella, Snow White, and Aladdin.
Staying onsite will be great to take a break in the middle of the day and then head back to the parks. We always went back to the hotel for naps after lunch and allowed for DD to stay up later in the evening.
If Buzz is a big favorite with your son then be sure to try and see the Toy Story Section of All-Star Movies. Daughter loved the big characters.
Have a great time!