Thank you for your suggest. I did it and found:

Pub. 17 :

Credit for child and dependent care expenses. The changes to the credit for child and dependent care expenses implemented by the American Rescue Plan Act of 2021 (ARP) were not extended. For 2022, the credit for the child and dependent care expenses is nonrefundable. The dollar limit on qualifying expenses is $3,000 for one qualifying person and $6,000 for two or more qualifying persons. The maximum credit amount allowed is 35% of your employment-related expenses. For more information, see the Instructions for Form 2441 and Pub. 503.

Pub. 503:

To qualify for the credit, you must have one or more qualifying persons. You should show the expenses for each person on Form 2441, line 2, column (d). It is possible a qualifying person could have no expenses and a second qualifying person could have expenses exceeding $3,000. You should list -0- for the one person and the actual amount for the second person. The $6,000 limit that applies to two or more qualifying persons would be used to figure your credit unless you already excluded or deducted, in Part III of Form 2441, certain dependent care benefits paid to you (or on your behalf) by your employer.

So, my taxpayer didn't have any benefits so his limit should be $6,000.

I'll try to put $0 as an amount for the other two children in the info  worksheet. It might help.