We always bring our seats. Both my kids use a CARES restraint on the plane.

Some will argue voraciously against this, but the car seat techs say you're not supposed to check car seats because of the unseen damage that may occur to the seat. You know how roughly baggage handlers treat suitcases- they'll do the same to the car seat and that could cause structural damage to the seat.

FWIW, we'll be in a similar situation with kids who are 4 and 6. The 4 year old also isn't 40 lbs yet and he's nowhere mature enough to ride in a booster anyway. I'll probably haul one of his Radians with me or buy a Harmony Defender for the other end and have it waiting. I wouldn't rent a car seat either. My 4 year old is very tall, though, so seats like a Cosco Scenera are too short for him.

OP again. My 5 year old is only 33 lbs so I definitely don't feel comfortable with him in a booster.

I really love the CARES harness, but my kid stopped using it around 4, so I wouldn't buy it if your kids are 3 & 5.

How close on 40lbs is your older kid? (Like close enough that he'd be 40lbs by the time you got there?) If you can swing a booster for the older, life will be much easier. OTOH, if you are driving a lot, and if there's a chance the kiddo will want to sleep in the car, a booster is not a great idea.

Oh one more thing - the cares harness was the biggestwaste of 75.00. My child wore it once then refused. If you think your child will stay put, invest. Last flight (month ago) ...we were visited by the flight attendant. Ah joys of a toddler.

When we were in an infant carseat we briught it with us, but also had a paid seat. For the toddler carseat weve rented. We essentially drive to a resort and thats it. Weve done it a few times. Its too much to bring it but if we were driving a lot, id probably check ours.

OP here, thanks everyone for the very helpful advice. We will be doing lots of driving once we're there, since my in-laws live about an hour from, well, everything. I'll look into safety restraints for the flight - we've never used them before.

It depends on how long I am staying at the place plus WHERE I am staying. The first time I traveled to relatives' house when my child was 18m, I took a costco scenera and left if there for future trips, even though I was just staying for one short week at that time.

Otherwise, when we traveled for a one week vacation or less, I just rent it.

If you will be driving much at the other end, I'd definitely bring your own seats, because you can use them on the plane (which is what FAA and NTSB strongly recommend anyway). Get either a Traveling Toddler or a cart and just strap the seats to that. The caution with rental seats is that their histories are not known--in addition to not knowing how other renters have treated them, you don't know how the car rental place treats them (and occasionally places have tried to rent expired seats because they don't know to pay attention to that, so double check that). If you are just driving a few miles at the other end, I'd probably worry less about it.

Alternatively, split the difference and just bring the Nautilus; use it for your three-year-old on the plane and get a CARES harness (good for children up to 44 lbs) for your five-year-old. Assume if you rent one seat it should be relatively easy to get one that fits your three-year-old, and you'll know you have the Nautilus for your five-year-old.

You can also consider getting a lighter travel seat if your budget allows; the SureRide weighs half of what the Roundabout weighs and is often under $100. If you are looking at renting a seat for any amount of time, you might make up the difference to that (or to the even cheaper/lighter Scenera, though it's also smaller so your boys might be close to outgrowing it) pretty quickly.

Finally--are you going for vacation, or to visit family? If the latter, you might also look into having a cheaper seat shipped directly there and having them meet you with it at the airport. Then it can live there if there are other children who would use it, or you can bring it home with you and at least be saved taking it one direction.

Never rent a carseat. You have no idea what it's been through (vomit, poop, an accident etc...). Bring your own. If you are not going to use them on the plane just check them with baggage (or gate check them). It's the safest thing to do to bring your own seats. There are some lighter versions you can buy cheap (Scenera for about $40 and I know there are others). Safety trumps convenience IMO.

Rent.

We bought cheap, light Cosco Sceneras for flying/rental cars. For the older boy, I'd probably take the Graco as a high-back booster.

We've rented car seats twice. Once when DD1 was almost 2 and then, recently, when DD2 was 6 months. The only slight hiccup was that the infant seat that Hertz gave us for DD2 was awful. Really flimsy and I couldn't get it to install correctly. But we went back and got a convertible car seat (one of the ones that is good for 8 to 45 pounds) and installed that instead. No complaints after that. I'll keep renting seats with cars in the future.

Depends on where we're going and how much other crap we're lugging. It also depends for us on how much driving we'll do once we arrive at our destination. For example, we did a trip that involved at least 2000mi of driving from site to site a few years back-- we lugged our car seat with us. But more recently we went to a tiny tropical island where we knew we'd drive a maximum of 2 mi a day for a week. We rented there.

My husband and I are flying to the Midwest with our 3 and 5 yo boys. Our younger DS rides in a Britax Roundabout and the older DS just moved over to the Graco Nautilus 3 in 1 because he is too tall for the Roundabout but does not yet meet the 40 lb minimum for a booster seat. We know that if we rent we will have to choose between a seat that is slightly too small (like the roundabout) or a booster. My husband would prefer to rent the car seats, even if it means putting older DS in a seat that might not fit properly. DH does not want to travel with our seats: Schlepping both carseats through parking lots and airports is difficult, especially since DH had back surgery in January and can not do much lifting/carrying. For me, though, safety trumps everything else and I'm willing to deal with the inconveniences in order to have our own car seats.

What would you do?