An important issue that we would need to address is gravity. Someone who was born and raised on the Moon or on Mars would likely not be able to function on Earth, because their musculature would be too weak. If we want a colony, we should probably develop artificial gravity to help sustain normal development, lest its inhabitants become permanent outcasts from the blue planet.
Aye, that will be a problem but it also seems like a fairly easily solved problem without the need for fake gravity. Strength suits when they first get back on Earth and/or exercise for a few months before the planned visit. Or just suffer for a few days while you come "home" to bury grandpa (or whatever) then hop back into space.
I guess I did make it a little complicated. Another alternative would be to base their economy on professional sports, so everyone there is a trained athlete and should be on roughly equal footing with your average Earthbound human.