ICT Tier 2 Dependant Visa for kid born in the UK

Hi,

I am currently on ICT Tier 2 Long Term visa in the UK. The current permission to stay is valid until Feb 2019. My organisation has decided to give an extension beyond this date which means that I would be eligible for an extension in November this year (extension can be applied three months prior to the expiration of the existing visa).
I have three dependants (wife and two kids). My younger son was born in UK earlier this year but doesn't have a UK visa as we were not sure whether we would be staying in the UK after the current visa expires. And since there is no need for a UK visa until there is a need to leave and come back, we decided not to file for his visa.

Now that we will be filing our extension, I wanted to know whether I can file the visa for my son (born in the UK) at the same time as we file our extension. I checked the rules for PBS Dependant visa on the UK government website and found the following - "If you are applying as a family member of a PBS migrant and your last grant of leave was not as their dependant or you are a child born in the UK, you will need to demonstrate your relationship". I have my son's birth certificate that will take care of this and I think this should be sufficient to back his case.

The work start date on my CoS (Certificate of Sponsorship) would be around the date when my existing visa expires (Feb 2019). Will it be ok to submit all our applications at the same time (in November) or do I need to do something else and what would be the visa start date that my son is likely to get.

Looking forward to some help/guidance in this regard.

Thanks,
Abhi