And that is what happens most of the time. BUT...if there are a lot of families that are boarding with young kids, in between the A and B group, then they will enforce the one parent/one child rule. It's always best to plan for the worst case scenario..then be happy when it doesn't happen that way.
It's very hard to tell a family of 8 that they can't all board together with just the one child under 4, while they just watched other families of more than 2 boarding together. It's kinda hard to say 'Well the rule is one parent/one child but they only had 2 addtl people, so we let them all go together. You just have way too many people over the allowable limit'.