the fire retardant stuff you buy and spray on-washes back out-so simply a waste of money---since most charities want you to wash the quilts before you send them.
also buying the flannels that are made for childrens sleepware (fire resistant) those (wash away) after a few washes too---so don't worry about it- make the quilts sturdy- washable and cute---they will be much appreciated...you know their clothing is not fire resistant---other than store bought sleepware and that washes away ---
the only thing to worry about with donation quilts is that they will hold up to (abuse) many washings/drying---and they are not going to get (special care) often they are tossed into big industrial washers- and hot dryers- make them to survive.