When boiling alcohol the alcohol should not get stronger and instead the boiling of the alcohol should actually make the alcohol less stronger.
Boiling alcohol or heating alcohol removes and evaporates some of the alcohol so that you get less drunk off of it or at least need more alcohol to get drunk when you boil it.
Just like when you cook food with beer or wine the boiling or heating up of the wine or beer helps evaporate some of the alcohol.
So that makes it safe for kids to eat foods that are cooked with wine or beer.
I've eaten foods cooked with beer and wine when I was 3 years old and above and it never caused any issues with me.