Having flown with four different carriers and a child varying in age from 4-weeks to a year and a bit, they're all basically the same, tho with a young child I have to say I was very pleasantly surprised by EasyJet out of Belfast Intl.
The main difference with Ryanair seems to be the seat scramble, so I suppose if there was way to ensure you get seated together then that's a good thing.
Ryanair flights seem to have fewer empty seats and people carry on much more due to the baggage costs, so if you're carrying a lot of hand baggage expect to hunt for overhead bin-space. If you're late to the gate, expect to deposit the various members of the family in a number of centre seats scattered from front to back in the plane. The cabin crew aren't interested where you sit so if you want to get someone to move, its a DIY job.
I read here how many people are giving out about Ryanair but, if you do it exactly according to their rules, it is cheaper.
Trouble is that it can be difficult doing it exactly according to their rules, which are getting stricter, especially with younger children.
If you think you need anything more than their most basic package, then that's when the fees start and it's no longer as cheap or convenient as it looks.