I was a dive boat operator. We had a no children policy, because children require child sized lifejackets, which we were not required to carry, children require watching, which is not why the crew is there (they are or should be watching divers), and when the poopoo is hitting the fan, little kids are easily launched into the bulkheads, staunchions, or over the side as adrenaline rushes and crew hustles.
Children have no place on a dive boat, but if you are chartering the whole boat, you won't inconvenience those of us who happen to not like children. Yes, there are actually people who work offshore so that they don't have to be around poorly trained small humans. Bring lifejackets to fit the kids. Real SOLAS or USCG Type 1 lifejackets. Those crappy west marine types likely won't cut it. Remember, your dive boat answers to a higher authority than the customer. They have to wear type 1's. In some states, all the time if younger than 8. Second, bring a nanny. The crew are not babysitters. Well, all divers need babysitting, but that's for another discussion. The crew don't need anyone to watch aside from the divers. The nanny needs to watch the kids. Bring something to keep the kids occupied. I'm thinking narcotics, but games and toys may work.