It's highly unlikely that anybody will care: you're got the right names, the right number of seats and paid the correct fare. At last check Ryanair boarding passes don't even distinguish between adult and child, unless it's a lap child (not the case here). So odds are very high nobody will even notice, and in your shoes I would not do anything.
That said, Ryanair is famous for being bureaucratic and unreasonable, so there is a small but non-zero chance that you will encounter a pedantic ID checker who notices and raises a fuss. The only way to avoid this would be to do a double name change, but that would cost a minimum of €35/flight/person.