"Set X Data Parameter on entity spawn", "Spawn entity as baby", Procedure when breeding is successful.

This is a fairly simple idea. There should be three new procedure blocks in the World Procedures->Actions section, basically it would work as the normal "Spawn Entity" block, but you would be able to specify if you want a Logic/Interger/String data parameter to a value. You could also use a checkbox in the "Spawn Entity" procedure blocks that would allow you to spawn the entity as a baby, which would only work for animal entities of course.

The other procedure block idea would be the "When Entity Breeding Success", This would help with many entity spawning procedures, for example, an egg-born mob like the Turtles or Sniffer. This new procedure block would override the spawning of a baby entity that's used as a default. Either that or you could check if you want the entities to spawn an egg Item rather than a baby when they breed.