I told my son when he was in first grade about St. Nicholas being real, but not some Santa that traveled around the world in one night. Honestly, I just didn't feel comfortable making up tales after he got suspicious. Of course, he went to school and told his classmates. His teacher wasn't happy with me.
When my sister and I were in third grade, we found some toys that Santa was supposed to bring us in a closet. When we questioned our mom, she said she didn't want Santa to lose them off his sleigh. But now I wonder if that could have been a good time for her to 'fess up.
So, no, I wouldn't recommend telling anyone's kids about Santa. You wouldn't get put in jail, but you might get beaten up by some mad parent!