Is there a reason to change dd's car seat?

[Dancergirl]

Dd is 4 and still in her baby car seat, ie forward facing with 5-point harness (Maxi Cosi one, can't remember the exact model).

Height wise her eye line is nearly at the top but not quite and I don't know how much she weighs but she's quite petite so nowhere near the 18kg limit I'm pretty sure.

So should I keep here in this seat for now or put her in a HBB? She's my 3rd dd and I honestly can't remember what I did with my older two. I know the 5-point harness is safer but she seems to be the only one of her peers still in this seat.

My 4 year old still in car seat as she too is of slight build. I have asked advice on this and been told that as she is safer in this to leave her as long as she fits comfortably.

Her BF is also still in car seat so I just assume it's the bigger children that have moved onto boosters.

I was told in mothercare that the boosters were all being discontinued as they aren't as safe as full car seats. The lady I was talking to didn't particularly seem to know a lot though so don't take my word for it!! (disclaimer-I'm v far off this my baby is only 7months!)

NoTeaForMe, the lady in mothercare was presumably talking about booster cushions, not high back booster seats that the above posters are referring too.

I moved ds1 when he was approaching the 18kg limit, and his head was above the seat, so I possibly should have moved him earlier. I know a number of four year olds still in five-point harnesses. I also know plenty of children moved too soon, so I wouldn't base a decision based on what others are doing.

I'm also curious. I have a DD who weighs well under 13kg and is nearly five. She's not tall (about average) but her head is at the top of the seat and she is just nowhere near being the right weight for a booster. If she's anything like me, she may get to be 15kg around 6 or 7.