How long did you keep your kids in convertible car seats? DD1 is 3.5 and still happily rear-facing in her Nextfit. She's only about 32.5 lbs and was 38" at her 3 year visit so I know we'll have some flexibility. I'm mainly wondering whether to buy a new convertible seat for DD2 or make do with an annoying back-up convertible seat + infant seat (we should have another 6-8 months and we also have a travel seat we can use for a short while if needed) until she can use DD1's Nextfits.
I'm guessing we'll switch DD1 to forward-facing at 4+ depending on her weight. Is there a benefit to switching her to a harnessed booster-type seat at some point (5 or 6?) or is she safest in her convertible seat until she outgrows the limits?