Kid friendly aps that work on iphone running 4.2.1

Looking to give my phone to my sons age 3and 4.

Can't seem to find any aps that work on this phone.

Can I filter my itunes search to only things that run on this version or older?

Is there an easy way to tell other than downlaoding and then syncing only to have it fail?

Do you know of any good kid friendly aps that would run on this version?

Thanks