Hello and welcome,
You are wrong on smaller planes being easier to handle. The truth is larger planes are more stable in flight, can handle more wind and are easier to see in the air.
As has already been mentioned a local club will usually give free instruction for the price of membership.
This is not a hobby for sons only, I just soloed this week at the age of 47 and am working with my daughters now to get them flying. It would be fun for both you and your son to learn together.
There are many options as far as trainer aircraft is concerned and it all depends on your budget.
There are alot of used trainers out there for low cost if you look around. Some clubs maintain their own trainers that they will let you learn on.
Best of luck.