Trust your software on this one. 

If a kid is born on Dec 31st, is it treated any differently for earned income credits or child tax credits than one born 11 months and 30 days earlier?

Anyone that was alive in 2020 qualifies for the entire RRC, dont worry about when they were born or died.

Thanks everyone!

@IRonMaN   just opened a 2nd shop. Be sure to take him up on his offer.

Word travels fast!  The painters are heading over there on Monday to paint the building puce.

I have a question along the same lines. My client is divorced . He and his X alternate years claiming their son. X claimed on the 2019 return and received the Stimulus payment for herself and the son. I am claiming the son on my clients 2020 and the software is giving him $1,100 when I reconcile the Stimulus payment. Am I missing something here???

That sounds right. Again, dont worry about 2019, Dont worry about what the other parent may have recieved.
2020 is the eligible year. Whomever claims the child that year is entitled to the RRC. If YOUR client didnt get any advance for that child, they get it on the 2020 tax return.

"I'm not sure if the IRS is splitting hairs on children or not!"

There is nothing to split in 2020. Only the fact of Year 2020 has meaning.

"I am claiming the son on my clients 2020 and the software is giving him $1,100 when I reconcile the Stimulus payment. Am I missing something here???"

Perhaps it would help to review what is really happening:

The funds were paid out as Advanced payment against a projection. The projection used 2018 or 2019 tax returns. But 2020 is the Actuals. You use the 2020 return to reconcile what a person is entitled to, against what they got.

If the person is not a dependent in 2020, then they would be entitled to the payment/credit as individual filers. That doesn't mean "not being claimed." It means "no longer qualifies as a dependent."

You might want to bookmark these links and read the IRS guidance.

Interactive wizards portal for determining dependency:

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

And:

https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-a-eip-eligibility

https://www.irs.gov/coronavirus/second-eip-faqs#Eligibility

One for each EIP.