Hellobee Boards

I wasn't sure whath a 3 in 1 was, so I had to look it up, but it sounds like a car seat that starts from around 20 lb and grows with the child until booster seat stage. Whereas a convertible would start at a lower weight range and wouldn't turn into a booster later (but you should be able to use it until they need a booster).

We have Britax convertible car seats, and I'm still using them with my both my almost 2 yr old and almost 5 yr old. We also have a convertible booster for my DD (5 pt harness booster that turns into seat belt booster later)