Car Seat Help!

We will be arriving in the UK for a 2 yr work assignment this coming Monday.

I am completely lost as to which is the best seat to purchase for my children once we arrive.

My son is 15 months old and 23lbs.  My daughter is 3.5yrs old and 36lbs.

Anyone have any recommendations?

Try Mothercare?

http://www.mothercare.com/b

Or try Which? for Car Seat comparisons:

http://www.which.co.uk/baby-and-child/baby-transport/reviews/child-car-seats

HTH.