I don't know how old your kids are, but I'd say do a lot of research on bottle calves, and be prepaired before you go pick em up. Have some of the main necessary medications on hand, instead of gettin home with a few bottle calves and have them get sick and not have a clue as to how to treat them. Baby calves go down hill fast when they get sick. Explain to your kids that sometimes baby calves dont make it.
It's well worth the cost of raisin calves, for your kids to be involved in the experience. You probably won't make much money on them tho. When we have a calf we hafta bottle feed, we always get the medicated milk replacer. Less chance of it getting sick with it. Also we put calf starter ( a pelleted feed ) out as soon as we get it goin good on the bottle. Not a whole lot at first, about a half a 1 lb coffee can. Then as it learns to eat that gradually increase the amount (directions are on the bag) After about 30 to 45 days on a bottle you can decrease the amount of milk given until they are on just feed.(Or you can continue to bottle feed as well for a few weeks, it won't hurt. ) A little hay in the pen for them to nibble on as well. And always fresh water.
If you are planning on buyin from a dairy, I'd ask around and find one that lets the calf stay on the mama a couple days before they are pulled off, that way they've got the colostrum and have a much better chance of surviving. Hope this helps.
Bottom line tho.....raisin critters is a great way to keep your kids busy, and they learn so much from the experience.