I found when I looked at the details in the parish records of my family's 'job lot' baptisms that also on the same occasion a brother had a batch of his children 'done'.
So I guess they would make a family occasion of it.
And often, I guess, that by the time they got round to having one chrisitened, perhaps waiting for a brother or sister to have thier baby so they could make it a joint 'do' , then the next one was on the way, so they then thought they may as well wait for that one to be born too. By which time the brother/sister was expecting their next one. By the time the occasion finally got arranged, each family had 2 or 3 children.