When do you put a 4 YO into a booster seat?

[CDMforever]

My 4yo DS has a built up type car seat and was wondering today when he can safely go into a booster seat?

it is much safer to remain in a high backed booster (do you mean switching to a booster cushion without the back?). My nearly 8 yesr old still uses a high backed booster seat and will till she is tall enough (135cm) to do without it

i would keep him in a harnessed seat for as long as possible (ie, until he outgrows it either height-wise or weight-wise)

then use a highback booster.

Ok.
No, he's definitely not outgrown it yet.
It was more a matter of having 3 DCs, a 5 seater car and 2 huge car seats in the back.
My poor 13yo is always so uncomfortable!

Our emergency booster seats (for when dh heads off to work with the highbacks in the wrong car) actually take up more bottom space than the Britax hiliner highback boosters but less shoulder space.The dc wriggle on the booster seats too.

Looking at moving our 4 1/2yr old into a Britax Adventure Car Seat (Billy) - anyone used one of these?

I have just got a bubble bum booster seat it is very narrow. I got is I can't get three high backs in the car. I would put the oldest one that still has to sit on something on it in the middle. I figure they gain side impact from the two seat either side.

On their web side it gave the width as 35cm put it is not it is much narrower. Sat my 9.5 year old on it yesterday and she said is was really comfy.

He can legally go into one when he weighs 15kg, but I agree I'd be trying to keep him in the harnessed seat as long as possible! If his ears are level with the top of the seat or he's over 18kg then he's too big for it and needs to go into a HBB or booster.