my girls are all adult; mama ~3, the other two ~20mosIf you gave the coconut meat, you need to make sure they have chick grit (crushed granite) available free choice.
Pasty Butt is when poop accumulates and blocks the vent. Sometimes it's accompanied by constipation, but most of the time it's poop that has stuck and blocks the vent.
Some common causes are stress (usually from shipping), being too hot or too cold - so taking time to watch behavior to see if your chicks act cold or too hot is a very good idea. You brooder should have enough space where the chicks have 1 place that is warm (heat lamp, brooder plate, mama heating pad, etc.) and the rest of the brooder is cool or room temp. (at least). Food/water should be on the cool side. If you watch chicks with a Mother Hen, they do not spend all their time under her. They run about, eat/drink, play, explore...the chicks run under her to get a quick warm up, then they are off again. They do nap, so they may be close to a heat source or even under it (or Mom) for a while, but then they seem to snooze and zoom...
Fun to watch and there's always something new to learn.