When Do You Switch from Convertible Seat to Booster?

Well at 18 months your son can (and should) still be rear facing, to keep him as safe as possible.
When he reaches the rear facing weight limit of his BLVD (either 33 or 35lbs depending on when the seat was made) then he should be turned around. Depending on how tall he is, he may be able to use the BLVD till he is 4 or 5. (Kids outgrow the Britax convertible seats at all different ages, most don't actually hit the weight limit for the seat, they just get too tall.) Your son will outgrow the seat when the tops of his ears are at the top of the shell of the car seat, and when the straps are no longer at his shoulders when they are at the highest setting.

When he is forward facing full time (and really at 18 months and 26lbs I wouldn't be comfortable with a kiddo forward facing just yet) then you could look at the Britax Frontier, it is a forward facing only seat that harnesses to 80lbs and then converts to a really awesome booster. The Frontier is for ages 2 and up though (Britax is really big on the extended rear facing too, that's why they've bumped up the rear facing weight limits on their newer seats) so you've still got some time before he will be able to use that seat. The Frontier also good for 9 years of use from the date of manufacture, so it could also be passed down to future kiddos if you wanted. :-)

Another option when he is forward facing would also be the Graco Nautilus, the harness goes up to 65lbs, then converts to a high back booster, and then it can also become a backless booster later on as well!

Hope this helps a bit!
If you have ANY other questions about anything car seat related, please don't hesitate to ask.

At 2 years old we took my older daughter out of the convertible. We bought a car seat (five point harness) that converted into a booster. It was an Eddie Bauer something or other (sorry, it's been a while). The new car seat should say what the weight requirements are.

This is not the safety-super response. This is just the "I have 4 kids and this is what I've always done" response.

Usually, rear facing till 1 year. Then, forward facing with 5-pt harness till 4 years (or 40 lbs). If they are 4 years old but still less than 40 lbs keep them in the harness until they hit 40 lbs.

Then, use a booster seat till 4'9" tall, but that could be a while. Typically, they guideline is use a booster till 8 years old or 80 lbs. However my daughter is almost 9 and weighs 65 lbs. If I kept her in a booster till she was 80 lbs then she would be there till she was 10 or 11 and I think that's too long.

ONe last thing: The booster seat is only for shoulder belts. If you use the middle belt (lap only) then you don't need to use the booster seat. Yes it is ALWAYS more safe to use the booster with the shoulder belt, but if you are in a pinch and your child is over 4 years old and you don't have a booster with you (like riding in a friend's car) then just put him in the center seat.

The minimum requirement to move into a mooster is 40lbs. That is the MINIMUM saftey standard. My daughter's car seat will allow her to stay forward facing in it until she is 60lbs. She that is where she will be until she out grows it. If your ever in an accident, you want them in the 5 point harness. It is by far the safest thing.

Hi Jessica,

I'm sure the convertible carseats last until atleast 40lbs. I have a Britax Decathelon and it lasts up to 65 lbs. My 5 year old nephew came into town and still fit comfortably in it. So I believe the Blvd does just about the same weight. But to get to your question, we are in about the same boat because I have a 2 year old and a baby girl who is about to turn one and grow out of her infant seat. So ultimately I am looking for one final seat as well. After doing some research I think I am going to purchase the Graco Nautilous. It has the five point harness for up to 65Lbs, then is the belt positioning booster and then the backless booster. So I believe this goes up to 100lbs. I saw it at Babies R Us and Walmart for $149. Not a bad price and it doesn't look bad either. I am a fan of Graco, but you can also check it out at the website. Hope this helps, sorry for rambling!