Tier 2 dependant for new born child in US

Hello.

I am originally from Russia and currently have Tier 2 general visa till 2019. My child will be born in US approximately in June.
Could you tell me If I can bring him to the UK as US citizen without any visa just with his US passport and apply for his Tier 2 dependant visa in the UK or I have to apply for his Visa in his home country (US) firstly?
Will be I able to apply for his UK VISA in the US If he is US citizen and I am not?

Many thanks

he cant come here on visitor visa as the ECO will know he is not visiting but intending on staying. Even if he was allowed, he can not apply for dependent visa after being admitted as a visitor.
you should apply for his dependent visa from usa and then come to uk. You will need to statement of £630+ for 90 days and the statement at the time of applying should not be older than 30 days.