Recent research confirms what we have long thought – rear-facing car seats are best for kids. Carseat manufacturers have been accommodating these rules for a while now, and children can safely stay in rear-facing seats upwards of 40 pounds. Sometimes these recommendations are frustrating because parents think kids are much happier facing forward. The truth is, most kids have no idea that there’s an option until we tell them. So keep them backwards until they don’t fit into the limits of their seat. This should keep kids backwards until they are at least 3 or 4 years of age.
Here’s a good summary of the recommendations with links to other information: