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 / do。
