It might be related to another mod, have you tried saving and reloading the game, I heard it can fix it sometimes. Also, do you have 'Young can't work' enabled in the mod-options and have them born younger?

It might be. I'm not too sure how it all works but i don't have any other mod that messes with traits or skills. I do have the 'Young can't work' enable and made them born at the age of 1 due to the birds and bees mod

Baby & Children mod*

Ah ok, I am not sure if the mod works well right now (I don't think it has a 1.2 version yet) - otherwise it might be normal, at least if they are very young with the option and also that mod, you can try to disable 'Young can't work' and see if anyting changes, you should be able to turn it on and off in a game without issues (may need to save/reload)