Not sure any of this will be helpful, but here goes.
I’m a lefty and my father, a righty, taught me how to put on tefillin. I put them on just fine.
I learned to use a righty can opener with no trouble.
With scissors, I always got the kind with big handles. If you turn them upside down they work just fine in the left hand. (Hence the big handles, so the fingers fit in the hole made for a thumb.)
Most kids learn silverware through imitation but I don’t remember how I did it. I’ll ask my two right-handed parents and get back to you.
Re it being a mum: I couldn’t find that in Mishnah, Gemara, or RaMBaM. In adddition, many people will tell you that your son cannot be a sofer based on a misreading of a Rema in hilchos tefilin which says that if someone wrote with their non-dominant hand, the tefilin are pasul. That means a lefty can be a sofer as long as he does not write with his right hand.