HSMP - FLR and child over 18

Hi,
I am currently in the UK on a HSMP visa valid until December 2009.
My wife and children are still in South Africa, but I want to start the process of moving them over here as well.

The dilemma:
My 1 child is currently 17 years old and turns 18 next year before my visa expires. If I apply for him as a dependant before he turns 18 it should be granted without a problem ... but what happens when I apply for FLR when my visa expires - he will then be over 18 - will he also be granted FLR? And possibly ILR when I eventually apply for that too?

I was reading some of the immigration law stuff on http://www.ukba.homeoffice.gov.uk/polic ... les/part8/
and came across this under the section “Children of Tier 1 Migrantsâ€

It's essential that he initially applies for a HSMP dependant visa before he's 18.

Children wrote:In order to be given entry clearance or permission to stay, a child must meet the conditions set out in the immigration rules at paragraph 319H of part 8,

For settlement, 319J applies, including

319J wrote:(d) The applicant must not be married or in a civil partnership, must not have formed an independent family unit, and must not be leading an independent life.

Thanks.
So it all sounds very do-able then.
Will ensure I get the visas for them before he turns 18.

Another question: Do they only have up to 6 months to enter the UK after the visa has been issued?