When I use a spawn egg that has a baby variant like a zombie or a villager and I click to spawn them really fast, then only baby variants spawn.

When I use a spawn egg that has a baby variant like a zombie or a villager and I click to spawn them really fast, then only baby variants spawn. If I made it so a zombie spawns with armor and then I click really fast, it spawns a normal baby zombie. I knew about this for about a year