It might sound extreme, but that's what Gen Y-ers in Spain have been doing for years — and resorting to legal action when their cash-strapped folks say no.

While the 2014 case of American teen Rachel Canning suing her parents was considered an anomaly, in Spain it is far more common for young people to expect handouts to continue into their 20s and even their 30s.

Under Spanish law, parents are required to support their children until they reach financial independence, with no age limit, and a string of cases in recent years has cemented the rule. ...