I have a 3yr old and one of 18mths. They both sit in car seats fitted to a LWB A Series, J Reg. That we've had almost a year.
Both the seats are britax ones. You may need to get a big car seat, with the baby inserts, as the small car seats, designed for new borns, can look a bit small in there.
For what it's worth it was worth all the while
It's something unpredictable but in the end is right
I hope you have the time of your life
Green Day - Good Riddence (Time of your life)