Tier 2 General dependent visa with 3 yrs COS

Hi. I would like to seek help in this forum. I am applying for my son's dependent visa who is turning 18 yrs old this coming may. I am a tier 2 general visa under under shortage occupation ( Nurse). I started my work in the UK last Jan.21,2019. I have COS of 3 yrs contract and in my COS details indicated that it was tick YES to certify maintenance for migrant ( and dependent if applicable).
I already have my 2 months payslip. I also have my BRP id. Do I need to provide bank statement? if yes, how much is needed? I am anxious because my son is turning 18 years old very soon. Pls. Help. Thank you very much..

"Each dependant must have £630 available to them whether they apply with you or separately. "
https://www.gov.uk/tier-2-general/family-members

Thank you for your reply@mamoru01. Do my son need the £630 even I have fully "A-rated" sponsor? and my COS details state that they certify maintenance for any dependent..
Thank you for your help. Really appreciated it.

I'm actually not sure as we are also just in a process of applying for Tier 2 visa.
But it probably won't hurt to over prepare as you are on tight schedule.