From your ChessKid account Home screen, hover over "Connect" and then select "Friends":
Type your Friend's username in the top search area.
Once you see your Friend’s name appear, click on the menu (the 3 horizontal lines) and select Add to Friends:
You should only be friends with kids you know in real life. To add a friend, your friend will ALSO need to repeat the steps above and send YOU a friend request from their own account.
Your ChessKid Friends will appear in the Friends tab in Fast Chess, where you can challenge them to a game if you're both in Fast Chess at the same time. They'll also appear in the Friends tab for challenges in Puzzle Duel if you're both in Puzzle Duel at the same time. You can also send Slow Chess Challenges directly from your Friend's profile page.
If you're trying to connect with an Adult account:
You can only be "Friends" with Adult accounts that are your Primary or Secondary Guardians.