I make excellent crab lemongrass tarts... kind of like a quiche. Or if you're looking for simple a cream of crab soup is really easy (basically stock, crab, onions, cream), and great with a loaf of bread and a salad. The other way we eat it around here is over pasta with lots of butter, garlic, onions.
If it's in the shell, I serve it in the shell. If the LO's are going to have difficulty with that, I would expect to help them or clean a couple legs just for them. But most kids I've met like trying to suck the meat out of the shell, and they enjoy getting messy/playing with their food, which crab is great for.
In the shell, I usually roast it in butter and garlic and white wine. Serve either over pasta or with a loaf of bread.