Increasing the time a child can safely stay in their convertible seat is a big issue and Britax engineers have come through in a big way with the introduction of the Britax Marathon with LATCH car seat. A LATCH Compatible Convertible Child Seat the Britax Marathon can be used rear facing 5 to 33 pounds and forward facing from 20 to 65 pounds. Compare the numbers and you will see it is hard to find a seat with these weight limits that is safe and functional.