I dunno.
We have the "Compass" boosters.
And a Britax "Parkway" booster.
Anyway, my kids are 6 and 10.
My 10 year old daughter, can still fit in her Compass booster.
She doesn't have to be in it anymore. She is a tall girl etc.
My son, is a tall/solidly lanky built dude, and he is in his Britax Parkway booster just fine.
Both my kids are tall for their ages.
My son by the way, is 6 years old and is 4'4"" tall and about 50-53 pounds.
Oh and LeeLee, so what what your MIL says. Or your Husband.
Eeew, I would be so irked with a MIL that tsk-tsks me all the time.
Well, don't they all?
LOL
ETA: okay so my 10 year old daughter can still fit in her Booster. And she does use it sometimesl. Her friends, many of them do not use their booster anymore. Sure, they don't have to be in one. But even my daughter said, she'd rather be safe. And feels safer, in it. Many of her friends just sit in the front passenger seat. Short or tall. Big or small.
Our friends 10 year olds, sit in their booster too. They have Britax boosters.
I was in a car accident once, while my son was in the car... in his booster. I am SO glad, he was in, his booster.
In your State... per laws, do the passengers in the rear seats, have to have their seat belts, on????
In our State, only recently did they make this law.
If not, people who sit in the back seat, would not be wearing seat belts.