I think you can avoid it if you get a particular type of prepaid credit card and pay with that, I'm not sure though. If you can reasonably avoid traveling with hold luggage, that saves an absolute fortune because luggage charges are staggering (rather than check in a case at Christmas, my mum sent all mine and DP's presents after us in the post because sending 18kg worth of parcel via international mail is cheaper than checking it in on a Ryanair flight). Don't get their insurance either, arrange your own, much cheaper. Priority boarding is a complete ripoff too, although I guess you might want it depending on the age of your children.
Bring your own food for the flight if you want some (you're only in the air for about an hour anyway so you can probably cope without) and if you want drinks, buy them at the airport once you're past security rather than on the plane. Everything they sell on board is horrifically overpriced.
They are very, very strict on hand luggage size and the 'only one piece of hand luggage' rule - I saw them trying to make a woman who had a handbag and a coat slung over one arm check one of them in. She, rather sensibly, put the coat on, and suddenly it was fine. If your bag looks like it might be oversized they'll make you fit it in one of those luggage measuring racks before you board and if it won't go in they'll make you check it in and charge you your soul, your firstborn and your income for the next 20 years an outrageous amount for the privelege.
That said, if you make sure you're aware of all their rules and clever ripoff moneymaking schemes, they're fine. They'll get you from A to B for a comparatively small amount of money, usually more or less on time. Don't expect luxury or any sort of interesting experience, but it's not harrowing either.