If you are happy with the 505 and you have the programming software/cable, that's probably your best bet. You an set them up the way you want for your kids.
The price is kind of high, but probably your best bet for a legal Part 95 radio that isn't a BaoFeng. But then again, if your kids are hard on things and you expect to be replacing radios frequently, then a BaoFeng might be a good option. But I'd probably choose a bubble pack radio over a BaoFeng. I think the quality control will be higher and it would be easier to return.
One thing I found with non-technical users, keep the programming really simple. It's surprisingly easy to get an "over programmed" radio into a place where it won't work and getting out of that can be difficult for inexperienced users. I often set up radios so all channels are programmed identically and the only real functions available to the end users are on/off/volume and push to talk.
Functions like 'lock' keys can be really helpful...
As they get more comfortable with the radio, you can carefully open up features.