How do I summon a baby mob?
You can make a baby mob by applying the appropriate spawn event in the /summon command.
For drowned and zombies, it is minecraft:as_baby, and for other mobs, it is minecraft:entity_born.
To summon a baby zombie or drowned:
/summon <zombie/drowned> X Y Z minecraft:as_baby
And to summon a baby animal:
/summon <entity type> X Y Z minecraft:entity_born
This does not work with villagers due to a bug.