[KiwiHopeful]

We brought ours on the plane, too. They are a bit pricey here and IMHO not of the quality you would find in the US.

One thing to note is if they are booster seats or car seats. Air NZ wouldn't let us use the booster seat on their flights, so it just got stowed in the overhead. It wasn't really a problem, and allowed my 4 year old to curl up like a cat in his seat to sleep. You'll want to check to see if the model(s) you have are approved for airline use. Otherwise, you can probably check them for free or just carry them on and stow them.

I also noticed that the cars here don't have the LATCH system, so you'll want to make sure you have any extra buckles or anything you need to be able to fasten them with the seatbelts. (Pardon my ignorance, but do you even have LATCH in the UK?)