I'd be hesitant to give them an internet connected device for entertainment purposes; not when there's great and cheaper alternatives (smartphones / tablets are relatively expensive). I'm thinking a Nintendo console or handheld - I got a new 2DS, it's pretty great. Those new mini models are pretty neat too (nes, snes, playstation is coming out soon, n64 is sure to follow), although I dunno if kids these days would enjoy them as much as we did the original consoles.

TL;DR: Don't let your kids play free games or consume free content. There's always a catch.