In the 1850 census there's a Daniel Standley listed as if he's William and Martha's son. He may be a son of her previous marriage to a Kennedy. It's hard to tell for sure since the 1850 census doesn't give relationships.
1850 United States Federal Census District 15, Carroll Co, Missouri (living in the Uriah Standley household) William Ha? Standley 20 m farmer born MO Marth A Standley 23 f born KY Daniel S Standley 3 m born MO