Who do I talk to about this. Oop

I baby sit a little boy. He definitely very behind in his age range hes 12 months and he cant do anything a one year old can do. Hes still on formula and other things he cant hold himself up or walk. Which is a little concerning but its honestly not that bad. But what gets me mad is I've been watching this boy for only 2 weeks M-F 6-5. Since the day hes came to me hes had very very bad diaper rashes n I've always treated them the best I can with the time I have with him. He always seems to get better by friday but monday comes n he has it again. Today is monday n his rash was so bad when he came to me idk what to do. I dont want to call CPS cuz idk if it's something worth doing to that family if shes not a bad mom. He goes to daycare next week so this is the last week hell be in my care. I attached a pic . I've been treating him with desitin I have at my house . This is at 4 pm this morning it was so much worst!!

**Edit: Yes I've talked to his mom as it's only his mom. But like I said I can only do so much. If she would wipe his ass she'd know he has a rash I really shouldn't have to tell her anything but yes I have an I will definitely be talking to her again today as it's so bad he has bare flesh.it makes me sad to see this and I dont want to call CPS obviously as I have no reason other then a diaper rash to be concerned and some bruises sometimes but it's normal for kids to have bruises. N I've also thought it being the diaper brand I know since I've watched him hes used huggies and luvs so I'm not sure**

**edit 2: I talked to her again n she said hes getting a rash because hes teething n itll go away soon she gave me some A&D ointment and that's it. I deleted the picture for the people concerned. I have an 18 month old n hes never had a diaper rash. I've babysat kids with diaper rashes before but never this bad. and I understand the concern about posting someone else's baby on the internet I was just very concerned and I didn't want to get cps involved if I didn't have to that's why I asked for help n posted the pic and scribbled out his private part. so its understood how severe it is, my apologies.***