My son had his tonsils and adenoids taken out this February, five days before his third birthday. His doctor had him stay in the hospital overnight for observation due to his age. The worst part of it for me was when the anesthetic was wearing off after surgery. He was too young to understand what was going on - he hurt, there were strangers around, he had an IV in his arm and a tube by his mouth delivering water vapor to make breathing easier - so he was understandably upset. Be prepared for a lot of lap time at first. To keep him occupied, we took a few coloring books, two or three small cars, and a portable DVD player with his favorite movies and a few new ones.
Food was a little difficult as none of my children like jello but he did like the slushies the nurses made for him: take a Popsicle off the stick, break it into pieces and warm it slightly then mix it with a little bit of Sprite until it gets slushy enough to eat with a spoon. (Too bad he decided frozen things were too cold for him to eat when we got home.) He also liked lukewarm chicken broth. I wouldn't suggest things like milkshakes unless he eats them with a spoon - the doctor said no drinking from straws (can't remember if it was for one week or two) as it might interfere with the healing process. I think he lived on scrambled eggs, chicken broth, mac and cheese, and (later) McDonald's cheeseburgers - I remember everything was yellow/orange and his appetite was not what it usually was. He hated the taste of his pain medication. Mixing it with a tablespoon or two of juice seemed to help but it still took some tough love to get him to take it. Liquids were the most important. If he didn't drink enough, his mouth would get dry and his throat more painful. This was mainly an issue at night. I definitely agree that waking them up for medicine (and a drink) during the night is very important.
The hardest thing was trying to get a three year old boy to not be too active when we got home and to not cry. Crying would make him cough which would hurt his throat and make him cry and cough harder.
I almost forgot: the hospital where his procedure was performed had a policy that children under four had to sleep in a crib. He had been in a toddler bed for months by this time but luckily he didn't get upset not being able to sleep in a "big boy bed."
Just remember they heal fast at this age and won't remember how much it hurt after a month or two. My son doesn't remember much of it at all after five months. And try to keep your patience if he gets cranky or changes his mind every two minutes!
Good luck - I hope everything goes well!