For kids I would recommend an older, calmer horse to start with rather than a young untrained one. You may want to lease a horse before you buy one as a trial to see what is involved in taking care of one. Do you or the other kids take riding lessons? Do you plan to keep the horses at your own house or board them somewhere? You should look up local barns and ask them questions about how much it costs since it may vary from area to area. Good luck!