Ryanair cabin bag question

[Oopsididitagain12]

It's been ages since we have flown as a family and we are heading to Dublin for a few days. I have paid for the two cabin bags for each of us but we need a car seat for our son as we will hire a car from the airport. I was going to let him bring the trunki backpack booster seat we have as his small bag, but the dimensions (40x36x16) are a bit different (slightly larger overall) to those Ryanair quote (40x20x25) Has anyone ever taken one on a flight with them? Are they flexible about allowing them? Otherwise, we will have to count it as his larger bag, I guess, but that's a bit limiting.

Car seats are free and don’t count as baggage.

Thanks so much, but when I looked, that certainly seems to be true for infant car seats with their own 5 point fastening, but less.clear for booster seats, which is all we have. I will call and check the position though, so thanks again for your reply.

OP if advise you to get it written on chat. Car seats are free (I think the age limit is under 12 but they echo the EU legislation) BUT tend to have to be checked in via oversized luggage into the hold. I have packed two booster seats in a car seat bag and sent them that way? For example, I travel with two under 3 frequently with a buggy. Even though it is cabin sized, it gets tagged and taken at the gate unless I have paid for it as a priority bag.

https://www.mumsnet.com/talk/_chat/4529065-Can-I-take-a-Trunki-on-a-Ryanair-flight

I know the above is about normal trunkis rather than backpack boosters but I think the same theory applies. They don't always enforce the limits but when they do, they come down very hard. You will always have people say they've done it and it was fine, but that doesn't guarantee you'll be fine.

Maybe put his stuff inside a thin bag, like a cotton shopping bag, inside the backpack? If they say it's oversize then you can check it as a carseat, and keep his stuff with you as carry on. You may even be able to open up a large cabin bag and stow his trunki bag inside it if it needs to "disappear".

Booster seats count as car seats with Ryanair, I've taken one like this before.

Take it to the luggage check in and check it in there, since it's too big to be carry on luggage.