M.D.
LOL - when my daughter was about 26 months, my SIL got married and wanted her and her hubby's niece to be ring bearer, but the other little girl thought she was supposed to be a "ring bear" and was very upset that she would have to wear a costume. My SIL ended up getting little bears to tie the rings to instead of a pillow.
20 months is a little young to do this on his own, I think. That aisle will look pretty big and intimidating. Is there anyone who could do it with him? It's not traditional, but could he walk down the aisle with his mom or right in front of her?
Rehearse multiple times with him as well. If I think of anything else, I will edit.