From a bride's perspective (as you refer to your "DP" i'm assuming you're not married and haven't had this), a guestlist is a complete PAIN in the arse. We're sorting ours out at the moment, and you do start thinking "how much do I actually like this person? Maybe I should just start being really pissy with everyone to reduce the guest list", and then you snap back to reality, but it is very difficult. You're having to think of who to invite of your own friends, what level of attachment warrants an invite, then family members, and then you start getting into parents' friends etc. (particularly as for us DP's parents have very very generously offered to foot most of the bill, so then there's the question of whether or not my parents are able to invite as many people as DP's parents as they're not paying for as much etc etc.) ... you get the picture. Then you start working on timings, and then add on that friend and family's children, who sits where, what to do with the children and so on. It's very difficult.
For our wedding, at the time of the wedding only one couple (out of our friends) will have children (and they tend to use weddings as an excuse to go without them, as lovely as their DCs are) and then the rest are children of family members. I started fretting as we're planning on starting the reception at 7, 1 hour of aperitif, pre starter dancing (it's the French way apparently), which means you're not sitting down to starters til 8/8:30 and DP informs me that it's not unusual to be having desert at midnight. With lots of Dcs around, they're going to be tired, hungry and annoyed. Also, our venue charges for DCs above 2 y/o, at 50% the adult rate, up until they're 10, then they're counted as full adults and you're charged the full price. So all in all, we're limiting the number of DCs to only immediate family members.