Thanks for the response! I was so thrilled to find this website (both for the advice and to see that we're not alone in our chaos of 3 in carseats)

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To answer your question - our older one is 2.5 and weighs 31 pounds. I think that the
Radians actually go up to 65 lbs (or 80 lbs) depending on the model and even the
Roundabout goes to 40 lbs so he'll be ok for a long while.
Anyone else have any other advice/thoughts?
Adriane
PS - what kind of minivan do you have? We rented a Toyota Sienna when my parents came to visit and I loved that we could put our whole family (2 adults + 3 kids in car seats) AND my parents. Plus, there were 2 latches in the 3rd row which was GREAT for us!