Right-Handed but I growing up I ate, wrote and painted (I'm an artist) Left-Handed. I can switch hit easily in baseball, But I've never been able to throw welll left-handed.
When I was learning baseball there was a great right-handed mitt that was well broken in and was a great glove, And my dad bought me the only left-hand mit he could find, It really was a good glove but it was just stiff and not broken in, And I hated it and so I used the right-handed. Love and never learned how to catch left-handed.
Interestingly, I developed essential tremors in my left hand and writing became very difficult and so I switched about 10 years ago to right-handed writing and eventually I now write very clearly right-handed.
When I made that switch in writing, I noticed that some personality traits that I didn't like about myself started to Fall away and I attribute that to using a different side of my brain.
Without a glove toss a ball to your kid over and over again and have him catch it without any love, And have him throw it back to you anyway that feels natural. If he does it better left than go in on left. If he does it better right then go in on right.