How to give a friend carseat advice.

I have a friend who has a 4 yr old daughter. The child is probably 40ish lbs 42inches and I think she turns 5 sometime this fall. They go to my church and I was babysitting her daughter last school year.

I knew she was already putting her in a booster but I didn't realize until she posted a video on facebook what kind etc. It's some sort of backless booster. It totally floored me how poorly her daughter was sitting in it. She put a video up of the little girl singing a song in the car while they were going somewhere (the car was moving) She was kind of sitting sideways with one knee bent up and was playing with the shoulder portion of the belt...pulling it out and over her head etc. She may as well have been sitting on nothing or not wearing a seatbelt at all because had they been in an accident it would've done nothing to protect her.

What do i say? Or should I say anything? I have given information to other parents I babysit for and not one person has ever responded to it or chose to make safer choices so I am second guessing even saying anything anymore. I don't want people to think I am coming across as a know-it-all or like I am trying to tell her how to parent. I usually just say something like....
"Hey I just wanted to share some information with you that i learned about while looking for carseats for my kids....your child means a lot to me and I just wanted you to have all the information available out there to choose the seat for your child"

Then I usually send then the video of Joel and Belle.

Thanks for moving! Sorry about posting incorrectly!

I find booster advice easier than other kinds, because I can rag on my own kid. I say "I just never thought about it before I got into car seats, but the thing about boosters is that the kid has to be in position all the time to be safe. So do I, for that matter--no more feet up on the dashboard, oops. And I've got a kid who wiggles! I'm just not going to be comfortable with him in a booster until I know he's not going to fall asleep or reach through the seats to hit me ("Hey mommy! Hey mommy! Hey mommy!") or play with the seatbelt or reach down to get a toy he dropped... Every kid's different, but mine's active, so I think he's not going to be booster ready until he's 8!" That's not targeted at one particular video, obviously, but it's one way to bring it up.

I'm pretty much not lying here, maybe playing up my kid's wiggles a bit (he's easy and listens to me, just an active boy).