if you want to make money making quilts it is very important to discuss cost before any purchases or cutting a single fabric- people who do not quilt have no idea what goes into making one- i hope the person you made these for expects the $300 you spent already ---or you may be in for an unpleasant surprise---
and to expect more is kind of wishful thinking- all money matters should be discussed in the beginning.
since it is next to impossible to really know how long you will take to piece, quilt, bind ect- a "rule of thumb" for pricing arts & crafts is materials x 3---the fact that you spent $300 on materials really makes this an unrealistic amount for a kids quilt- in the future you may want to have the recipient purchase the fabrics/batting ect themselves- then you can just charge for your time.