Yes he's a whopper 18.6kg naked - v tall too (taller & heavier than all the 3.5yr olds I know)
So what do I do about the car seat?
The maximum weight limit for his seat - and all others in that group as far as I can see - is 18kg.
Is he too young for the next stage high backed booster with car seat belt? Was thinking of the Britax Kidfix? but gut feeling is he isn't old enough?