Most US parents said their children had encountered "issues" like bad language, sex or advertising online over the past year, but they are not stopping their kids' Internet use, according to a new study.

A survey by market researcher Harris Interactive of 411 parents of children aged between 6-18 who use the Internet found 71 percent said their child had at least "one issue" with the Internet in the past year.

But four out of five parents said the Internet helped their children in school and only three in 10 parents - or 31 percent - said their children spent too much time online.