Help! Need Carseat for My 4 Almost 5Yr Old Today!

Your best bet will be the Britax Frontier85 or Recaro Prosport, Graco Nautilus or Evenflo Securekid. These have a 5 pt. harness and will harness kids for a long time, with the Britax getting you to age 7 or 8, possibly. They also convert to a booster. Once the child turns 6 I would consider using a booster if the child was ready, but some kids might need more time. Note the Britax has the highest harness on the market. (We used the Prosport and my tall 6.5-year-old outgrew the harness, otherwise he'd still be in the harness; we converted to booster).

You'll want to use the booster until age 9-12...whenever the child fits the adult seatbelt and can 5-step. All kids are different.

I would put the 20-month-old rear-facing in the convertible seat.
Good luck!

If your older son is happy with his seat and not outgrown it, why not get a convertible seat for the younger one that will RF and then FF? My DD is 4.5 and was RF in her Marathon (ours only went to 35lbs but now they go to 40) til recently and the top end is 65 FF in our model year (now to 70). Britax makes other seats as well, often sold at Babies R Us. Please consider keeping the little guy RF til at least 2 if not beyond.

Graco Nautilus or Britax frontier

We've been using the Graco Nautilus since my daughter turned 1 (before the rear-facing til 2 came out) and she's 5 now. We still use it as the high-back booster with the car's seatbelt. I think within the next year we'll take it down to just the backless booster. I absolutely love that it's the only carseat she's needed for 4 years and will probably take her up to when she doesn't need anything else. My only complaint is that it's a bit heavy, and I refuse to take it out of my car. I ended up just buying a less-expensive carseat for when she travels with family members.

Britax Frontier is great! Forward facing only - five point harness till about 85 lbs, then converts to both a high back and a low back booster. It's comfy and works well and my son really likes it. Only trouble is it can be a pain to install. If you don't need to move it often, it's great.

Otherwise, the Graco Nautilus is similar and also good, and about $100 less. It's not quite as comfortable though.

Just bought a Cosco high back booster that also has a five point harness. It can be used with the harness or without. I am using it as a booster with seatbelts. Works great. Child will be six in the summer.

Your 20-month old should remain rear-facing for now. The American Association of Pediatrics recommends that children remain rear-facing until they are at LEAST 2-years-old, preferably longer. Get a convertible car seat that does rear-facing, and keep the 3-in-1 for your older child.