Washington and Custis married in 1759. So if they had any children, they'd likely be in their teens by the time the War for Independence began. Most likely, if they were boys they'd serve in some capacity in the Continental Army - probably as staff officers or if younger as messengers - not front line troops or combat officers. It is possible the eldest might serve in combat by the time of Yorktown.
They'd likely follow their father into politics, either as early bureaucrats or perhaps elected in their own right in the Virginia legislature or later Congress. Early America was a very cozy polity originally, and certain families dominated local politics. Washington's family could easily do that. However, it'd depend on their natural talents whether they achieved anything worthwhile. Washington likely would be very concerned that it not be seen that his children were becoming a dynasty or a kind of royalty. That would smack of monarchy and aristocracy, and it would hurt his own reputation.
Given Washington's own political instincts, his children would likely be Federalists which may help that party survive longer. If they were in the party by the Hartford Convention, I don't think they'd want anything associated with them that pointed to splitting up the country.
If he had daughters, then it's possible they might be married to some of the young officers he commanded in combat.