Wedding with kids. How many is too many?

TLDR: I’m freaking out that we’ve invited way too many children and I don’t know what to do.

My family is very small but my fiancée comes from a large Catholic family. He has nieces and nephews (5 in total) that I’ve known since they were born and we adore them. I have some cousins with kids (6 total) that we’re also close to. We definitely want to have them all at the wedding. Fiancée says we have to invite his entire family including their kids, most of whom neither of us have ever met. The guest list right now is 176 and 60 of the guests are kids. 60!!!! While the venue has the capacity for 200, I assume they mean relatively well behaved adults, not a horde of loud and energetic children. I don’t know what to do and I’m starting to panic. We really want kids there but this seems insane!! We’ve already sent save the dates with the kids included so feels impossible to backtrack now. Also, after many months of searching, we’ve already booked and paid a huuuuge deposit for the venue. Please advise!!!