Some hens are better mothers than others. The younger they are, the less likely they are to be good mothers. If the mother isn't doing her job, a brooder is definitely the best option.
Buttons tend to be better at taking care of their chicks than coturnix, but that is not always the case.
I would get them into a brooder as soon as you can. The ones that got chilled may well bounce back. I've had a few that I thought were dead come back after getting warmed back up.