Older Americans can be a burden on the economy — but for cash-strapped families, they’re a lifeline.

Roughly one in four adults 25 years old and over got $100 or more from parents in 2011, according to Judith Seltzer, a sociology professor at UCLA who analyzed Census data and the June 2012 Survey of Consumers. The average gift was $6,500. Better-educated parents were more likely to give: Nearly 37% of adults with college-educated parents received assistance.

Grandparents also provide child care. About 28% of grandparents provided at least 50 hours of care per year for grandchildren they didn’t live with, and nearly one-third of grandmothers who live with a grandchild have primary responsibility for them. More affluent grandparents, meanwhile, tend to help adult children with mortgage costs, house down-payments and education, greasing the wheels of economic mobility for their grandchildren, research shows.

The upshot: Older people are quietly serving as an emergency-support system for adult children struggling with a weak economy and high joblessness — and indeed, with years of slow wage growth and declining economic mobility.