Super quick background: My mom has custody of my daughter currently.
My mom is allowing my daughter to choose between a low-back booster and a high-back booster. I don't want her in anything but the high-backed booster....which is why I bought it in the first place. Alivia will be 7 in November, but is only about 40" tall and is about 43 pounds. She didn't transition into a booster in general until after she turned 6. When I say anything to my mom about this, she says that Alivia's doctor said it was okay.
Please point me to valid information proving that high-backed boosters are safer! (We live in Wisconsin, if it matters.) Or is this not worth a battle? Am *I* wrong? Is she just as safe in the other booster?
ETA: The car seat I want her in is the Graco Nautilus.
There isn't much evidence either way.
I personally prefer to see 7yos in high-backed boosters, but it isn't an issue I'd press, especially if your mother has the legal right to make the decision.
Okay, then that's what you should argue. If she cannot use a backless booster properly, she is not safe in it and needs a highbacked booster.
I just read your ETA in the OP. Do you want her in a harnessed seat or a highbacked booster seat?