My Chi, Cali, has an open fontanel and it's quite big ... about the size of a thumb print. She is 2 1/2 years old and so far we have not had any problems with it. I do have Cali checked out by my vet twice a year instead of once a year (but she usually goes more often than that because she is prone to getting colds very easily). Hubby and I are extremely careful with her and we do NOT allow anyone to hold her.
So yes, your dog can live with an open fontanel but you and anyone who comes in contact with your dog must be very careful of it. I would definitely talk to your children about it and teach them how to properly hold the new puppy and explain why they must never press on the puppy's head. Also, be careful when putting on clothes and harnesses so that they don't put pressure on rub against the top of his head.
By the way, hi and welcome to YT.
