R.J.
1) Yep. MO is an At-Will state... So dad can be fired
2) Unless the son is special needs (and needs that require supervision / care)... States follow the babysitting age, typically. There are extreme examples, but generally at 15 or 16 a child is considered old enough to take care of themselves (with a home, bills paid, food, etc.) for 90 days without there needing to be emancipation or other orders.
((15/16yos taking care of themselves (while in a paid for home, bills, etc.) is especially common in Oil Rig & Long Haul Trucking families... Where parents are gone 1-3 months, home 1 month, gone 1-3 months. As well as reservest families, with single parent being gone for short periods of time (few weeks to a few months). Becomes an issue during deployments of 6+ months. ))
Know its not what you asked... But if it makes you feel better... I was serving in the USMC @ 17.