Does anyone have any personal experience with a baby that was exposed to meth during most of their pregnancy? What did you notice about them and their development?

I babysit a now 4 month old boy (had him since 1 wk old) and he's showing significant developmental delays but am not entirely sure if it's because of the drug exposure or because his dad is a new dad and may not interact with him very much at home. I try to play with him but the only thing he will do is smile. I have brought up the delay with the dad but as a parent I'm sure he wants to think there's nothing wrong which is understandable.