It needs to be a joint decision. This isn't something he should be deciding on his own, as it will greatly affect everyone.
Army life is TOUGH. It's hard on the married couple and it's hard on the kids. Some people deny this, but realistically *most* members are moved away a lot (every 2-3 years at least) and a lot of members spend great amounts of time away from home (not including deployments, which are 8 months long at a time nowadays). My partner wasn't in a job that deployed much and he still spent many months away a year on exercises etc. He worked a lot on weekends and public holidays. The hardest part though, was how regimented our life became. The army controlled everything - where we went, when we went etc. We were denied travel to certain countries. We had a holiday cancelled on us and were told to just get over it and get our money back from insurance (not the point). My DH was even pulled up at work for something an officer saw him doing at the shops (!) and it was all very controlling - some people like that...and some people don't.
There are benefits to being in the army though - subsidised rent, job security, free health & dental for your partner, lots of time off, other financial benefits.
You both have to weigh up whether the pros out weigh the cons.
Good luck. I hated having a partner in the army. Some people don't mind though.