If your child is always asking Google for how many days until a certain date, and that date happens to be their birthday, Google/Assistant/Nest/Home can tell anyone it recognizes the voice of how many days until their birthday.
Google will have to recognize the person for “how many days until my birthday,” but if you don’t feel comfortable with Google voice recognition of your kiddo you can add them as a contact with their birthday and then say things like “how many days until Maggie’s birthday?”
Also there’s Weather Frog on smart displays. I recommend it.
To get Weather Frog, on your phone open Google Home, find your display (works on Nest Hub and Lenovo Smart Display that I’ve tried, so probably every smart display,) choose settings, photo frame, experimental, you should see Google Weather Frog.
Throughout the day enjoy the random adventures of a frog just living his best life in the same weather you are.