Ideas
I’ve figured it out. You have to make sure the child is Happy with the green aura, and then the interaction ‘heartfelt compliment’ is available.
I will try this!
Edit post try: My child sim was energized, and the compliments option came up for her to give a compliment, which she did (give a pep talk) and it added to the formative moment count. I then tried to get her to give a pep talk to her other parent, but the compliments option had disappeared again
I am assuming you are therefore giving the solution, I will try get her to give another compliment when happy and report back.
Further edit: so far she has been over-energised, but I managed all the pep talks (ie compliments) and she achieved the formative moment. I guess the solution is that only certain emotions can enable children to give compliments.
Final edit: yes, my child sim could give a compliment when in the happy moodlet! :)