Question 99th percentile for height: high back booster or ff harnessed seats

My DD is 3.5 y/o, is 42" tall and weighs 42 lbs. Our vehicles have her in Britax Marathons and in an Alpha Omega elite. Can we comfortably move her to a high back booster, and if so what is recomended for a child who has consistently grown at the 99th percentile rate? Or should we invest in 3 ff harnessed seats? MHO is to keep her in the Marathons and buy her a new hbb to replace the Alpha Omega elite. Thinking about Britax Parkway, Recaro Vivo Lite and Sunshine Monterrey boosters. Please consider that she still naps in the car and that height is a limiting factor. Thank you for your kind assistance!

Hi and welcome!

She's still too young for a booster. The minimum for booster usage is 4 years old and 40 pounds, but most techs on this board will say that kids need to be 5 or 6 before they are ready to be in boosters full time.

For your daughter, I would recommend the Britax Regent. It has the highest top harness slots of any seats on the market. Even though she's tall, the Britax Frontier and the Graco Nautilus (which later convert to boosters when she's old enough several years from now) have high enough top slots that you might want to keep them on your list as well.

She needs a new seat right away to replace the Alpha Omega Elite (unless it is one of the new 50 pound versions), because it only harnesses to 40 pounds.

3.5 yo is really too young for a HBB. Kids should be at least 5 or 6 to be in a booster. For a bit more than the Monterey, you could get her a Graco Nautilus (I think Walmart is having a sale on them - some have gotten it recently for $144) that has really high top slots and harnesses to 65 lbs and then converts to both a HBB and LBB. My dd will be 4 in Nov and is 41 inches tall and 42 lbs and is in the Nautilus on the second-to-the-top slots. I foresee my dd would have at least another 1.5-2 years in the harness of this seat unless she takes a monster growth spurt. Another option that is a bit more money is the Britax Frontier. It harnesses to 80 lbs (but harness not any taller than the Nautilus's) and then converts to the tallest HBB on the market.

I agree with the previous poster, at just 3yo, your daughter really needs to stay harnessed for another couple of years. I understand that she is very large for her age. So is my daughter. She was 38 inches tall and 35 pounds at 2.5 years old when she outgrew the Alpha Omega harness by height (shoulders over top slots, second-to-top headrest setting). She was 41 inches and 40 pounds at 3 years, 4 months old.

Back when my daughter hit 40 pounds at 3 years old, there were very few options to harness her, either Britax 65 pound max weight limit convertibles, the Britax Husky (older version of the current 80 pound max weight Regent), or the now-discontinued 50 pound max harnessed weight limit Nania Airway. None of the 65# Britax convertibles made sense: she was too big to utilize the rear-facing function of those seats, and so tall and long-torsoed already that she needed the top slots, with little growing room (indeed; she was too tall for Britax 65# seats by 4.5 years old). We ended up with both a Nania Airway (for lesser-used vehicles) and a Britax Husky/Regent (for the primary vehicle). The Husky/Regent lasted my daughter until she was 7.5, about 54 inches and 70 pounds.

The Britax Frontier and Graco Nautilus are also good options to consider, choices that weren't available when my daughter was outgrowing standard 40 pound harnessed weight limit seats. She would have fit the harnesses of those seats until she was 6. In my honest opinion, the Frontier's belt positioning booster mode blows the Nautilus out of the water, so if I were in the market today for a seat for a 42", 42# child, the Frontier would most likely be my #1 choice, since it should last even the biggest of kids to age 5-6 in the harness, and it makes a much better booster than the Nautilus.

The Britax Regent is also still a good choice, though it is wider and bulkier than the Nautilus and Frontier, and does not become a belt positioning booster, it will harness longer (1-2 years longer for most kids).

How is she fitting the Marathons? Where are her shoulders in relation to the top slots? She will outgrow those seats by height when her shoulders are over the top harness slots. At her height, if she is long-torsoed, that could be anytime. If she is average or shorter in the torso, you could still have 1-2 years left.

How much time does she spend in the other two vehicles? My first inclination would be to move the Marathons to the two lesser-used vehicles, and get a Frontier, Nautilus, or Regent for the primary vehicle.

Having said all of that, my daughter did begin booster-training (meaning, less than 5 minutes per trip, with no other children in the car to distract her from proper booster behavior, gradually working up to longer trips when she proved she could handle it) in her dad's vehicle at age 4. I did not trust her in a booster any longer than 10-15 minutes until late 5, and she didn't move to a booster full-time until age 6. We used a Regent part-time (longer road trips) until after her 7th birthday. I would delay booster-training for at least another year, and even then, at 4.5, I would evaluate whether or not booster-training is a necessity yet. How often does she ride in these other vehicles? Do the seats stay in these vehicles, or are they uninstalled? Are there other children in these vehicles with her? Will there be long road trips in these vehicles? All of those questions, and I'm sure a million more should play into the decision to booster-train.