DD has just turned 3 and isn't 18 kg yet, but probably will be before 4. She is in RF Britax TWE in my and DH's cars. My DPs need a new seat for her in their car that can also take her older cousin (hence getting it now, not when she gets to 18kg). I'm not convinced in her going in a high backed booster which seems to be the next option. It is mostly the idea of the 3 point car seat being used rather than a 5 point harness. I don't trust her not to wriggle out or undo it. It has to be FF as it will be going in and out of their car and I don't think we could be confident of fitting a RF seat each time.
So, does such a seat exist?