Even though I may not use all the kids, I still try to get all kids. The main kids I use are Lucina (Robin's wife), Morgan (Robin and Lucina's kid), Severa, Inigo (Chrom's son), Owain, Kjelle, Noire, and Gerome. The other kids won't be used that much.
I currently don't have all of the DLC, so no one can go Bride or Dread Fighter right. Plus I never grind my character's level out because that totally takes the challenge out of the game. But I will try to get Galeforce for Inigo and Owain before I get them. Plus Severa, Lucina, Morgan, Kjelle, Noire, and Cynthia can all gain Galeforce.