Ah, I feel your pain.
I will however add some context in similar situations I have found myself in.
We have an iPad loaded with fireman Sam and peppa pig. It lives in an indestructible iPad cover that would probably survive a necular war. We also have Frozen earphones, which could be the most popular thing in our house. The child sometimes takes these out to play with without our knowledge. Every long haul flight we have remembered them no problem. There has been a couple of short haul flights where they have been forgotten.

I dont one know your situation so I can only describe my own. There is no amount of reasoning, bribery, scolding, pleading, begging, gin, brandy or whiskey that can calm my two year old like the sound of that bloody pig. I have played it before for her on a flight without earphones. I have kept the volume as low as possible. It may not be popular but I’ve taken the decision that the noise of that bloody pig is preferable to full scale fallout. This isn’t to say it’s right,I should always remember the earphones but sometimes accidents happen.

The flight from from Belfast is about an hour, which I’m sure you know well. If possible try not to let it bother you.

For or any parents I suggest a google of Scottish peppa pig, definitely NSFW and not for children’s ears.