Hi, I felt in a good position to answer this as we have just returned from a week in lanzarote with our 2 sons, the youngest who is just 3 and had type 1 for 7 months. We had booked our holiday before he got I'll and diagnosed otherwise I don't think we would have booked it after due to being scared to go probably, but because it was booked already we just went for it! We had the letter from our nurse to say what we were carrying and everything was in our hand luggage in case of things getting lost. Security was no problem, they didn't ask even to see the letter or any of his stuff we had.
The flight was fine, although on the way home it was delayed while we were sat on the plane and had to stay on for an extra 2 hours, but I explained to the air hostesses and they found him a meal which they didn't charge us for so that was great.
On holiday was fine we found. We were all inclusive so he could get anything he wanted, which was mainly the diet drinks they had. We did had to buy some Gatorade as he kept going low, but that was down to us not realising the heat would affect him so much, plus the fact we were way more active than at home. So he would sip on that through the day to keep his levels up. He also didn't eat for the week (fussy 3 year old!) but it was manageable due to him having the full sugar drinks in small amounts instead.
I think you will have a great time and hopefully lots of fun! I do remember it being pretty hectic in both airports without having much space or time to do blood checks, I think we might have appreciated a bit more time so we didn't feel so rushed so maybe allow a bit of extra time in case you need it?
Have fun!
Emma