We recently flew from BOS to DUB with a layover at LHR using British Airways/Aer Lingus. Each time we boarded, the allowed us ample time in the pre-boarding process to wipe our son’s seats down and make sure we were comfortable. We did not request any other accommodations so cannot speak to that. We packed our own food for him and he did well with that.
On our final leg home, the flight attendant in our section was amazingly helpful, bringing us a list of all the food served on board to suggest what our son might be able to eat (we politely declined as we didn’t want to try new food products in the air!). He also let us know they are fully stocked and trained with EpiPens and recounted a story of a recent time the flight attendants administered and EpiPen to a girl having a reaction mid-flight. He was friendly, understanding, and attentive. I would highly recommend flying with them!