I crate the youngest when I am away, the other is in a (mostly) puppy proof room with a baby gate (the crate is in the room too). I've let the first one free in the house without any problem, but they are used to being in another room playing most of the day anyway. I'm just waiting for Tips to be a bit older, but he doesn't really need to be crated anymore.
But again, we've been away more than 4 hours only once since we got the dogs.