When do children have to keep Meat/Milk laws of Kashrut?

It is forbidden to feed even a baby non-kosher food (if there is no health reason that requires it. If there is a health consideration, a halachic authority should be consulted). A child need not wait a full six hours between meat and milk and a one hour break is sufficient (Shmirat Shabbat Kehilchata, first ed. ch. 32, 39). As he grows older, he should be accustomed to waiting longer periods.