Do losses from my minor sons custodial account get counted towards a loss on my taxes

NO ... realized cap gains or losses are reported on the child's return only.   Only dividends, interest and cap gains posted on a 1099-Div can be entered on the parent's return if they choose to not file a separate child's return (which is usually better to do). 

No. The account belongs to your son, not to you. Sales in your son's account have to be reported on his own tax return, not on yours.

It would be a good idea to file a tax return for your son, even if he is not required to file, in order to establish the capital loss. It might not do him any good this year, but he can carry it over and it will reduce his taxable income in some future year or years. He should file a tax return every year until the loss is used up, to maintain the capital loss carryover.

The capital loss carryover is not tied to the custodial account. Even after you turn over the account to your son when he is no longer a minor, he can continue to carry over the loss until it is used up.