Edited to say, changed the lamp to the 250 watt in case anyone wondered
Hi Nicole, welcome to BYC!
Sounds like you have a nice flock started and it's great to get the kids involved.
There is a state thread for MI members, here's a link to get you there:
Chickens deal with cold weather better than heat but that's pretty chilly for young birds. You could put the 250 watt bulb in their coop and if they all stay as far from the heat as possible, then they are too warm. If they all cluster directly under the heat, they are too cold. What you want to see is the birds moving in and out of the heat.
Good luck with your birds. Nice to have you join us!
Generally young chicks are kept in a brooder indoors, with heat lamp (lowering gradually every week since hatch) until they are fully feathered out at 6-8 weeks. Otherwise they don't have a thermostat to warm themselves up. They need their feathers to insulate them. Downy fuzzed chicks don't have it yet.