Anonymous wrote:If you are exhausted more money will not fix that. Do you want more money or less time looking after this child. Figure that out before you talk to them.
This! To me it seems like you are starting to suffer from some caregiver burn out. Totally understandable, but more money is not going to change your duties or lighten your load. I do think it's fair for you to ask for a raise , but this isn't a situation of job creep and your family taking advantage of you this is the reality of the job caring for this child.
If it were me, and I am not you I would request more time off so that I could recharge more frequently over more money.
As pp pointed out with their child's medical expenses they may not be able to afford a raise and keep you full time.
Actually going part time might be a great solution some insurances will cover at least in part care by a nurse. They coul have a pediatric RN or LPN come in part time nd have you the rest on the time.