Car seat clips, am I overreacting?

I'm a nanny. I've been with this particular family for over a year now, and I watch two boys ages 6 and 8. I frequently take them to and from school, so I use their car seats when traveling. I know when you put the seats in your car you're supposed to clip them in using the clips in the back as a safety measure. I do this every time, and make sure they are secure.

Well today, I had to swap out their car seats with their father, and noticed he just set the seats in the car without using the clips. I casually mentioned that he should use the clips for the boys' safety, and taught him how. Afterwards, I texted the mother about it, and she said that she didn't use the clips either!

I feel that it's important to do these things to keep children safe. Isn't it dangerous to have a loose car seat in case there's an accident? Or am I overreacting? Does it really not matter all that much? Regardless, I'm still going to keep doing it, but I wonder if I should bring it up again to both of them or just leave it be.