Can I escort my nephew to his southwest flight since they allow a 12 year old to fly alone? It's a big airport and he has never flown alone. Much less had to navigate a complicated airport.

Not the best time now. Due to airport construction work outside the airport, the assistance outside airport is complicated and confusing and there is no proper service help that one can get. eg: the airport staff was clueless about shuttle services.

Not through security unless the airline can make arrangements. But typically no

You should check with the agent at the counter or call the airlines.