Tons of apps out there. I like all of the Kids Shapes, Kids Connect the Dotes games. There are several by that company. I like them so much, I purchased several - like $1 each I think. We also like Talking Tom Cat and any of the sister games.
My daughter also loves the puzzle and matching games. They are great for her memory.
There is also an excellent Learn to Read app. I forget the name but I purchased b/c it was so good.
Toddler lock is great but not for anyone over 2yrs old.
Zebra Paint, Kids Doodle, Air Control Lite, Kids Paint and of course Angry Birds.
Couple other suggestions.....
- Go Launcher has a "Lock" option that locks all icons and settings on desktop. Once enabled, no icons can be moved or deleted.
- Airplane Mode is great but disables a couple of the apps. I keep the ones that it does not disable on my phone because Airplane Mode is a MUST when you hand your phone to a toddler and are not looking. She has purchased about $5 in apps before I learned to do this more consistently.
- Create a folder of games and put it on your desktop. Rename the folder with your son/daughters name and teach them that is their folder - with their name. It helps them learn to spell their name.
- Add a link to your gallery in the kids games folder - unless you take raunchy pictures

. My 4yr old loves scrolling through the pictures - I have hundreds. I use my phone camera (in addition to the regular camera) just so there are pictures on there that she can scroll through.
- Another option (in addition to the Lock mode in Go Launcher) is to setup a whole new launcher just for your son/daughter. You could download a free launcher and set it up with game icons, fun desktop wallpaper, etc. You could even delete the phone icon so they can't call anyone and hide apps in the app tray. Put a hidden link to Home Switcher to move back and fourth between launchers. I just thought of this and will set one up this evening.....BRILLIANT!!!