I have a huge family with loads of little kids. It’s the total opposite with my fiancée.
We did a rough guestlist and there were as many children on my side (27!) as her whole list… 
So we decided all my siblings can bring their kids and (where possible) for the rest, just the parents get invites. But as we have so many people coming from Scotland (we live in Berlin, she’s from here), most parents will bring their kids too. So we’re setting up a sort of dedicated kids room for them to just go crazy in. 