1. Kids only know fun and not fun.
Make games interesting. Casual games should never take over a minute to mechanic. Ie play. Controls should be intuitive and have a purpose. Never add a control just because you can. Use colours that are lively and balance with the emotion you trying to portray.
2. UI / UX simplicity is the hardest thing to master.
Laying out the proper using interfaces should allow everything needed to be displayed, but not inhibiting the user to access it. Metro in WP7 / Windows8 is a great example of nice UI / UX design.
Allow for different tap and gesture abilities i.e. soft / hard taps, fast and slow swipes.
3. Implemental Challenge
This may be the toughest. Making a game challenging is easy. If the challenge isn’t balanced correctly, the player will find it to easy and lose interest or possibly, it’s too hard, again losing interest.
4. Audio
Your audio should tell a story. If your audio is narrative, you can teach the player and give them hints in game. You add higher pitches as points were you want to the player to jump low points when you want them to crouch or go down. Use audio to get the player into the mood you trying to create.
Final thoughts, this is by no means a final list. Just some thoughts that I wanted to share. Hopefully, I’ll hear your comments both good and bad.