It's up to you of course, but I wouldn't have a dog like that around kids. That's just my own personal feelings. Akita's are up there near the top of the list for most unpredictable and aggressive breeds. Not that that means every one of them will be so, but its worth taking into consideration. Other things I would consider are the fact that he tackled someone to the ground. Guard dogs are supposed to alert to a potential threat, not attack. The fact he jumped on a man without provocation or command from you is worrying.
Also, you need to be careful when surveying dog behaviours. Very often, what is taken as protective behaviour, is anything but in a dog. Google resource guarding as an alternative reason as to why he may have sat close to your friends baby. I have seen countless cases of babies, children and people killed by dogs, and whilst I don't think every dog is aggressive, I just want to be a voice of alternative thought because you've specifically asked for that type of opinion. I personally could never take a risk with a dog in the band of breeds known to attack. That said, many live with children and never harm them. Its entirely up to you to make an informed decision. Good luck x