Am I right in thinking that there is no age limit before which you mustn't put your child on a booster seat? We have a Romer King Plus (Group I) and my 25 month old has grown out of it I know my son is on the large size for his age, but they advertise it as being suitable for up to 4 years and if I plot him on the percentile charts for a 3 year old, he's below the 50 mark.

Husband has bought a booster seat type (Group II, Maxi-Cosi Rodi air protect). Now, I think he's too young (I accept not too small, he fits the height and weight restrictions) to be on a booster seat restrained by just the seat belt rather than a harness. My husband tells me I'm being paranoid. My parents tell me (they're in the UK) that it's illegal to have a child under the age of 3 not in a harness restraint. I've read the tcs brochure and can't see any mention of age of child, it just says they must be in a suitable seat. I don't like that when he wiggles, the seatbelt loosens, that when he slides forwards I can't get him back and he doesn't understand/know how to push himself back into the seat properly. We're going to be driving through France to the UK in the summer and would like to know if there's a way I can force my husband to accept he needs to be in a proper 5 point harness seat!