I think Motocrossing with your son would be about the best thing you could have told your wife. Especially since she has ridden yourself. You are not out drinking with the guys and chasing skirts. You are working evenings at home with your son getting ready to spend at least one day of the weekend out riding with and being with your children. How is this in anyway a bad thing?
Just spending a good chunk of money without discussion. That's out of character for me, and not something I would want her to do to me.
Mostly because motorcycles kill people, and mothers are averse to that happening to their children. Less averse to it happening to their husband after he buys their son a motocross bike without consulting her.
We already had his bike for a while. He's just now really interested in it. He used to only want to ride electric bikes, or bmx bikes. I spent the money to get myself a bike because I got excited about his excitement for the sport.
Anything kills people. I think learning how to operate a motorized vehicle before learning to drive can only help surviving on the road. But, I am old as fuck and what do I know.