dd had the same op in January, aged just over 2, and was very thin (from poor eating related to her large tonsils etc), and needed an HDU bed for a night due to also having a floppy larynx....so I totally understand you anxieties!
First, it was totally and utterly worth it and I'd do it again in a flash if I were in the same situation. dd now eats well, sleeps much better, and its a joy not to hear her gasping for air at night.
Yes, its horrid when they are under and you have to wait...dh was with me, which helped, and although I felt shaky and wobbly, it went quite fast. I held dd's teddy bear for 40 minutes (took longer than usual because they checked her larynx at the same time). TBH, the hardest part for dd was coming round - she was in pain and confused - because she fell asleep before they put her under and slept through the whole thing.
She never had throat pain before either - but I explained to her she was going to have an ouchy taken out so she could sleep and eat better, and that afterwards her throat would be sore but it would get better after a few days. I've no idea how much she took on board, but she seemed to grasp some of it - and was only concerned about whether Mummy would be there with her in hospital the whole time: obviously, I reassured her heaps about that.
If you're in HDU, you probably won't have a bed for the night for you, but I was able to lie on the bed next to dd and rest...better than the armchair, and she liked it. Nurses were lovely and very accomodating. I took a bag of snacks for me, cleansing wipes, clean tops (in case dd threw up on me, which she did once after the anaesthetic) and a couple of light, clean t-shirts for dd as she got very sweaty and hot (and a bit sick) that first night.
Foodwise, they recommend 'rough' foods like toast to help healing...I also thought of the drinks, but a) the chemist said there were none for 2 yr olds and b) with hindsight, they were unecessary and dd probably wouldn't have drunk them - she went off milk at one point during her recovery period and just wanted tiny bits of food, and water. She did get very thin, but I promsie you it doesn't matter - she was blooming within a few weeks of the op, and everyone comments now on how nice it is to see her with a round little tummy
I did give ice cream as well as rough food, and ice lollies to start with, because she wanted them and at least it was calories/energy - but amazingly, she was just as happy to eat bits of toast, crisps, ham. Mini cornettos, once home, gave her a bit of energy.
Some kids seem to bounce back very fast and have very manageable pain, others like dd have lots of pain - we gave round the clock volatarol and paracetamol suppositories, provided by the hospital because she wouldn't take meds (very young, couldn't reason wit her). It was hard work for a few days, but like I said, well worth it
Any tips you need, any support you need, just shout - there are lots of us here who've been through it (several needing HDU beds for various reasons afterwards, too) and will keep reminding you it'll be ok!