Most boarding schools do not offer early decision; it is not common, so there may not be anyone on CC with direct experience.
A few thoughts –
Schools offering early decision probably correlate with low endowments. Low endowments = not hugely generous financial aid.
Wouldn’t the ED decision be analogous to college? That is, if you need substantial financial aid, wouldn’t it be in the family’s best interest to compare awards? Especially since the majority of schools do not guarantee to meet need.
Also, although of course it is you making financial decisions and you are helping with the process, it is your child that is applying to the schools, not you.
Are you already set with your schools of interest, or would you like some input? If so, let us know what you are looking for, and why your family is considering boarding school.
Good luck!