Nearly $19 billion changes hands in America yearly as family members help one another--children aiding aging parents, mother and father helping offspring start a household--the Census Bureau reported. By far the largest share of the assistance is child support provided by adults--almost always fathers--to children no longer living with them. That accounts for 63% of the total, the bureau said in its first survey of monetary help exchanged within families. The study, called “Who’s Helping Out? Support Networks Among American Families,” found that $18.9 billion changed hands with 6.3 million people providing help of one sort or another to 9.9 million others.