You and your child can only play together after you have connected to their account through the Guardianship process. Check out this article to learn more: How To Connect To My Kid Through Guardianship
Fast Chess
From your adult account click Play on the menu at the top of the page and select Play vs Kid:
Click on the Friends tab which has the icon
Your kid must also be logged in, online, and in the Fast Chess area at the same time as you are for you to see them on the list.
Alternatively, you can search for your child by entering their ChessKid username into the search box at the bottom and clicking the magnifying glass.
Click on the icon to send them a challenge!
Slow Chess
From your adult account click Play on the menu at the top of the page and select Slow Chess:
On this new page, use the drop-down menu under Play to select the type of game or a specific opening you want to play. You can also check the Unrated box to make the game unrated so it doesn't affect the rating:
Click on the Friends tab to see a list of your friends, including your Kids
Select which of your kids you'd like to play and click Play to send them a challenge!