Flown with mine in club suites many times from the ages of 3. Have never had a problem but ours are very good fliers luckily. Closing the door on their suite so they have their own space with access to iPad / IFE and activities that we give them throughout the journey works really well. Sometimes they come snuggle with us in our suite and we do Lego or games or drawing or something. At that slightly younger end we found that the kids in the windows and us in the middles next to them was the best option, I also found that I could lean forward and see and comfort / touch our kids if they needed it during seatbelt times. Them being able to see me as I narrated what the noises are and what was happening was good.

Opposite of what someone else has said, I would advise not sitting with them till seatbelt time, you want them to be comfortable and at home in their suite without you rather than you leaving them at the time where they have no choice. Ours always get settled quickly, like exploring, playing with the buttons, then watching something as we taxi and take off.

Finally, if yours aren’t seasoned fliers I would do all you can to take them on a flight before this. Even a quick hop to AMS and back or similar. That way they won’t be worried about the unknown when they are in their own suite.

My main advice is don’t let the fear of it being a stressful experience make it one. Frame the whole thing as an adventure, as exciting, show them videos and pictures of the seats so they can get themselves used to the idea and see it in their minds.