Very big 5 year old...

I have a 5 year old who has definitely outgrown his existing seat. He just turned 5 and weighs 72 lbs. he is around 46”. Since he is growing so fast I am not really sure what to put him in at this point.

To complicate matters we just got a little surprise and have a newborn coming so we are going to need to do 3 across in an Infiniti QX60. My older daughter is still in her Radian R100 which I will convert to booster mode soon. She is 7 and around 60 lbs.

So does anyone have a recommendation for a narrow seat for my son and then a good narrow seat to use for a newborn for the 3 across? Thank you for your help!

Does your radian go to 80 lbs? If so, I would use that for the next few pounds and look into a dedicated booster for your oldest.

As far as I can remember, the seats that go to 80+ pounds are a diono seat (80), nautilus 80, and the frontier clicktight (90). Only the diono is on te slimmer side but at 72 pounds, unless you have one, I wouldn’t buy one for possibly 8 lbs. The other 2 seats are wide but the frontier is probably your only option for the longest use.

You could look at a ride safer travel vest. The large goes to 90 lbs, I believe. There are also the ez-on vests and harnesses that might be an option. Some of those go up to 150+ lbs. You’d need to install a heavy duty anchor if you got an ez-on but they walk you through it all.

Is there any chance that at 5, he has the impulse control to sit in a highback booster? If so, there are lots of options available for him. I had one kid that was fine at 5 in a booster and 2 others that needed a harness a bit longer, so it is totally kid dependent at 5 if a booster is an appropriate choice.

Hopefully someone will come in and add to the list of seats that go past 65 lbs. There may be another one of 2 but they are likely to be bulky as well.

The Britax Frontier puzzles quite well with the Clicktight convertibles. It might be worth trying out if you can.

Other than that, yeah, the oldest is likely booster ready (and could even go in a backless which would help- side note, I wouldn't use the R100 in booster mode, it doesn't do well.) And the 5 year old may well be, or you could consider adding an Ez-On 86-Y to a booster if needed.

He could probably do a highback booster. Are there two narrow highback boosters that would work with an infant seat? Is there any reason to not have my 7 year old in a highback booster as well? I think it would be easier if they have the same thing. Also any recommendations for an infant seat that would work with this? Last time I had a keyfit 30 that was great. Thank you again for the help!

A high back will take up more room. Also, the narrowest available booster is the Bubblebum, which is backless only, and you may need it to make it work. There are not a lot of narrow high backs out currently. The Harmony Dreamtime is probably an option but only for a short while, they're not tall. The 7 year old may already have outgrown it.
The Keyfit is a good narrow base that tends to install easily and it does well in most 3 across situations.

Have you considered using your 3rd row? It would simplify things for you a lot.

My wife wants to do 3 across instead of using the 3rd row. So how about a highback booster for my 5 year old, backless booster for my 7 year old and then the keyfit 30 for the newborn. Will that work 3 across? Any recommendations on which boosters to use in this scenario?