Booster seats?

What age can you use them from.

Oh and I both have seats in our cara but are forever taking them out for my mum and dad to use when they have Ellie.

I'm thinking of buying them a booster seat.

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it sounds like they need to be 22kg before going into a normal booster seat.
For Charlie we have a booster seat with a back to it, that's fine at there age.

Caleb is in a booster but like Kell it has a back to it as it was his 2nd stage seat aswell it converts all the way up to 7 years old

I got Tyler a booster type seat but it's from 9 months up to 11, it has a harness and when they are bigger can just use a seatbelt. it was from mothercare about 60 quid but you can get cheaper ones too x