We took the kids two years ago for their first (our 2nd) disney experience. I found a few ways to make their experience better .
Before getting there I purchased them each their own gift card with $30 on it from the
Disney store so if they wanted souvenirs they had the money and also had to decide how much they wanted it since they were spending their own money, worked great and I didn't have 3 kids asking for EVERYTHING they saw at each shop.I also purchased them each a princess or Minnie outfit on clearance to wear 1 day at Magic Kingdom on the day we went to princess breakfast.They loved this! From Party City I bought inexpensive disney trinkets and laid them out something each morning to discover including Minnie Mouse ears bought for about $5 less than the park charged. We heard alot about pin trading from others and how much fun it is for the kids especially (it was ! The kids and even us had a great time with this) so I bought some cheap lanyards at party city with princesses on them and to start everyone out I went to ebay and purchased a few bags of mixed lot pins they could use to trade. The pins they traded with cast members made not only great souvenirs but they had the experience of bartering and fun conversations meeting everyone and choosing which pins they wanted from the cast members.
Another thing I loved was finding and using Touring Plans , granted we went in late August but with that in hand and our fast passes we NEVER waited in line longer than 10 minutes. Look it up , it's great, you type in what you'd like to see/ride in each park each day , and it will organize your itinerary for the least amount of wait times and you can even schedule meals/breaks. We saw /did everything twice and had a few hours left over to just spontaneously wander.
I love all the others great tips and already found a good many to use if we get to go again.