I was given an overdose of magnesium during labor.could that cause behavioral problems with my child?

Effects are short : The effect of magnesium on a newborn are rather short lived. It does produce low muscle tone and can transiently cause breathing irregularities. I have seen some have brief periods of breathing cessation that required monitoring in the level 2 nursery. After the kid starts to urinate it leaves the system quickly & has no long term effect on growth or development.

Clear with your OB: Magnesium sulfate is given for a reason durung labor/delivery, when mom is experiencing symptoms that could hurt her and the baby that are not her fault, nor the doctor's. I suspect there was a nicu crew there to tend to any initial, transient low muscle tone or neurological depression in your baby. There should be no long-term effects from the magnesium. Ask your OB about your experience.