Help 以后是跟不定词bare infinitive / to-infinitive 的,所以help sb. Doing sth. 是不对的,只有: Help sb. to do sth. / help sb. do sth. 是正确的。 例如: I would like to help my mum do some housework. I would like to help my mum to do some housework. 意思上也没有太大分别,只是个人习惯/喜好用to do ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.