Put the kids on single player in a creative map and just let them create. When they get older, introduce survival mode.
Not quite sure how they got there, but I believe it went something like this:
1) Kids watch daddy play Minecraft and watch Paulsoaresjr's videos along with daddy. (Paul is very family friendly in his videos) They scream when surprising things happen.
2) Kids start playing around with Daddy's copy of Minecraft PE on iPad and eventually take it over.
3) Kids get plush Creeper stuffed animal with explosion noises from Santa and use it sneak-up and scare Daddy. Kids: (whisper) "Lets creep Daddy!" Creeper: "ssssSSSSBOOM!" Daddy: "Ahhh!" Kids: *Giggles*
4) Kids beg Daddy to let them play Minecraft on PC and eventually Daddy sets up a single-player creative world for them. Kids show-off their creations to Parents.
It's not all the time and as with any toy it goes in and out of their attention, but they are having a good time and I feel that it is beneficial.