So, the last migrant wave was huge (I went from 20 dwarves to 62), of which I had 3 rangers, 2 farmers, a cook (yay food-producing professions with all these new mouths), and....35 children! My population cap for children was 10:20.... My population is now mostly children and they are swarming my fort! My questions:
1) I'm guessing migrant waves aren't counted in the pop cap as far as max children?
Correct. The baby_child_cap only affects pregnancies/births inside the fort.
2) Do children count toward the trigger point for ambushes and sieges (IIRC ambushes = 50, sieges = 80 dwarves)?
Yep. Once headcount hits 80, you can get sieges, and children/babies count.. I'm not aware of any population limit for ambushes, i remember getting them with 30 or less dwarfs.
3) What the heck do I do with all these children? I have no massive deconstructions I need to do.
Check their ages, most will grow up in one to four years. Downside is, they'll grow up to be peasants with no notable skills, you have to train them from scratch if you want to make them useful for anything other than hauling. I actually like to do that, but opinions differ.
3a) Is there any way to cull the child population that wouldn't make people upset?
If you do this, i'll be very disappointed in you.
Oh, you mean inside the game? Probably, but that's so despicable i refuse to enable it. Parents can normally handle losing one of their children if they have enough reasons to be happy.
If you send the children on a vacation in the Goblin Happy Funtime Park (i.e. let them walk around and get abducted by goblin snatchers), the parents will not count the child as lost, the child will be happy to be free of their parents' soul-crushing supervision, and the goblins will be happy to have new happy citizens. Everybody wins!