I still have my 4.5yo in a 5pt harness car seat (Graco Nautilus). Is that still necessary? What do you do?
DD1 is still in her Britax Marathon. She has one more notch to outgrow on the height, and we'll keep her in it as long as possible.
I haven't really thought much about what seat we'll use after that.
It's not necessary, but it's safer...
I believe the Nautilus converts to a high back booster (basically remove the 5pt harness) then after that you can convert it to just the basic booster.
We have the Nautilus for both our boys. DS1 has been using the car seatbelt since he turned 4 last year. He'll be 5 next week.
DS2 is still using the 5 point harness and he turned 3 a couple months ago.
5pt harness is the safest option - i plan to use one as long as DS's will fit in them.
We have the Sunshine Radian 80's that go up to 80lbs in a 5pt harness... as long as they are fitting into that, they will have that seat.
We have started booster training recently and my older daughter's doing great. She's very tall and all torso and only has an inch of torso growth left before outgrowing her radian for height, so I knew we had to start getting her used to a booster sooner rather than later.
There are actually no studies proving a harness is safer than a booster if the child is old enough, heavy enough and mature enough to use a booster. In fact, in many places in Europe (including Sweden, which is the world leader for carseat safety) nobody uses a forward facing harness due to concerns about the safety of one (it puts a lot of load on a single point in the neck whereas a seatbelt dispurses the weight more evenly across the body and the delay in locking actually may cushion the body better than the tight harness). They use a rear facing seat until the child is booster age then go straight to a booster. Since my daughter has never slouched or moved out of position at all in her booster I'm letting her use it more and more and am quite confident she's safe since it fits well and she uses it correctly (we keep the radian in the car and she knows I'll pull over and switch seats if she misbehaves at all).
We actually are hoping to keep our younger daughter RF until she moves to a booster for this very reason and have a radian with a 45 lb RF weight limit to help with that.
That said, much carseat information is conjecture anyway. The truth is, since adding seatbelts and then adding carseats and boosters there have been so many fewer injuries it's hard to tell exactly what the "ideal" is and it wouldn't be ethical to run a real life study on this information. It took gather 25 years of data to determine that RF was safer and there's a bigger difference between RF and FF and FF versus booster.
After watching my friend's 5 yr old wiggle down until his neck was at the lap belt and his but was on the floor board (while she was driving) I've sworn to myself mine will stay in a 5 point until middle school if I can pull it off.
Seriously - he would have been decapitated if we'd been in an accident.
Both of my guys click both parts of their 5 point harnesses by themselves. The only thing I have to do is let them out.
It's not a big inconvenience in exchange for knowing they're as safe as they can be.
I'm in no rush to make a change.