I always wave to kids when they are watching the trains, theory being if I wave to them now they might not swat rocks at me when they get older!!
Always a possibility I suppose
and yes there are drivers who wave back which is lovely
I took a youngster in the half term to watch the trains and said if you wave to the driver sometimes they will sound their horns or wave back.
The child waved the driver sounded his horn - the child ducked under my jacket as they didn't realise how loud it would be.
After that there was no waving from the child