no need to worry about interaction when playing online games (except maybe with CamperStrike, the most retarded of all online games
).
The only thing you will have to worry about when playing BF2 online is exposure to language that you might not want your son to see. They can get quite colorful sometimes (very rarely, only a few idiots talk like that), but for the most part it is a pretty good gaming community right now.
To be honest, you should disable the firewall while he is playing. It could help with the lag. Yes, you are too paranoid. I keep my system on a DMZ in my SonicWALL when I am playing online games, meaning I am completely outside of my firewall. No worries.
Just make sure that if he gets into playing, that he -
1. Doesnt punish the commander when he gets teamkilled by artillery. It is the players own damn fault, not the commanders (most of the time).
2. if another player lays landmines and he drives over them with a vehicle anyways, dont punish then either. Its the players own fault
Hope he likes the game