C.M.
Hi M.,
I have been traveling to Ireland all my life...my parents were born there and my husband is from there so his whole family is there. What I have found is the best thing to do is to take a short nap once settled into where you are staying and then to stay up the rest of the day until normal bedtime. I don't really sleep on the plane so I need that extra bit of sleep. My husband is able to sleep on the plane so he stays awake until bedtime. I guess it all depends on how much sleep you can get in during the flight.
We traveled with our daughther when she was 8 months old, a lot younger than yours. But, from what I can remember from when I was your kids' ages, a little nap always helps...but not too long or they won't be able to go to sleep at night.
Hope this helps! Have a great time, it's a beautiful country!
C.