Thanks for everyone's input! I've decided to charge her the regular full time rate as playfelt suggested. Mom gets topped up from her job so her paying for a spot is not an issue. I truly do believe her when she says she intends on sending both her kids here. In the year they've been with me I haven't had any reason not to trust her or her husband and I do genuinely like them so I am happy that I will have them for quite some time still. I know what kind of parents are out there so I'm happy I have this family!