I need advice!

Hey! So I’ll try to be brief but explain the most important. I’m a nanny for a Russian family( and their amazing). Mom did say that she thinks her kids are behind developmentally since they speak Russian to the two boys and not English( the boys are twins and are 2.5 years old ). The issue I’m kinda having is that the kids bang their heads off everything. And when I asked the mom if they do that often, she shrugged and said sometimes. Well today when I was outside with them. One of the kids banged their head on the cement and screamed( obviously I ran over and grabbed him to make sure he was okay) but this isn’t the first time since I started working with him that he’s done this. I’ve never watched/ nanny for children that has done this.

I also have my associates for teaching and continuing for my masters, but we’ve never talked about this in classes and how to handle the situation.

So what do you guys recommend?!