The bug

For a baby villager, age < 0,  right clicking does not trigger the stat.talkedToVillager score which limits the ability to create baby villager dialogue mechanisms in adventure maps. 

To reproduce

Add a scoreboard objective as follows:
/scoreboard objectives add VillagerClick minecraft.custom:minecraft.talked_to_villager

Then show the VillagerClick objective in the sidebar:

/scoreboard objectives setdisplay sidebar VillagerClick

Clicking on an adult villager increments the VillagerClick counter but clicking on a baby villager does not.

Code analysis

Code analysis by Avoma can be found in this comment.