You need to use IRS resources. This has all the links for what you ask:

https://www.irs.gov/help/ita

I've already read IRS resources.  I believe that the taxpayer is entitled to all the credits but was looking for another opinion to either dispute or verify.

The child was born in September 2021?  He started living with her in August 2021, but was sleeping with her in December 2020?    Would due diligence include DNA tests?  

37 years in this business and I get these opinions.  Why do I even bother with this forum.

"I believe that the taxpayer is entitled to all the credits but was looking for another opinion to either dispute or verify."

Geez; you asked multiple questions:

"Can he claim the EIC"

"& Child tax credit?"

"Also can he file as HOH? "

No one except you knows their conditions and qualifications for each thing, so you would work through each ITA.

"Why do I even bother with this forum."

If you already worked through all three, is there something specific that makes you doubt what you got for results? Because you didn't tell us anything about that part. You simply ask three parts as if we can work through each one for someone we know nothing about.

Sure, people without kids are getting EIC.

Sure, people are getting EIC, and even using 2019 income for that purpose.

And no offense, but, it's hard to tell who the issue of HOH applies to, because there is no perspective in how it was asked. Both the client and the fiance might be "he" nowadays. I'd rather make no assumptions while trying to work through questions for which I have no information.

"Why do I even bother with this forum."

I don't know. It's not like you have ever helped anyone by answering a question.

Delete - it got posted twice.

I was just going to say, that was so good that you had to post it twice 😁

Fair enough.  Apology for not being specific.  Even though the conditions are met for each at the time the child was born what made me have some doubt was the fact that the parents did not live together for the entire year.

Well, now we are getting somewhere.  Yes, the child was born, not adopted or placed in the home for foster care.  And the POSSLQ's are the actual parent.  Why do I bother trying to answer questions when so many facts are deleted to trick people into a wrong answer?

Shoot, I put Aug baby, not Sept, but the ITA for Filing Status includes:

"Did Baby live with you more than half the time he/she was alive?"

and:

"Did Baby provide more than half of his or her own support for 2021?"

and:

"Was Baby single as of the last day of 2021?"

and:

"Did you and Baby's other parent live apart at all times during the last six months of 2021?"

Just go through the steps.