Re: Developmental Delays in someone else's child? Need advice.
I agree with a pp who mentioned using the physical illness as a way to get him to a doctor. I'd just tell the mom that in order to have the child back in your home, state legislation requires you have some sort of documentation that the child has seen a pediatrician for the ringworm and coughing (even if that's a little white lie). You might mention, at the same time, that the shaking and drooling concerns you a bit and that she might want to mention it to the doctor when she has him looked at for his illnesses.
A pediatrician *should* notice the delays. If they aren't taking him to well visits then no one has anything to go on. That's what well visits are for. Not saying everyone has to do them, or you're a horrible person if you don't or anything, but it is what they are intended for.