Foreigners often make some strange mistakes in Chinese when they study the most difficult language--- ---Chinese. We try to analyze typical sentences to correct these errors.

         Sān gè nǚháizǐ men bǎ xiānhuā sòng gěi dàibiǎo le.
False: 三个女孩子们把鲜花送给代表了。
          Sān gè nǚháizǐ bǎ xiānhuā sòng gěi dàibiǎo le /nǚháizǐ men bǎ xiānhuā sòng gěi dàibiǎo le.
True: 三个女孩子把鲜花送给代表了/女孩子们把鲜花送给代表了。

英语名词加-s表示复数后，名词前边还可以加数词，如three daughters。在汉语里，指人的名词加表示复数的词尾“们”后，名词前边不能再加确指的数量词，这个句子要么去掉“们”，要么删去“三个”。
In English, a noun pluralazed by the suffixes may also be qualified by a numeral, e.g. three daughters. However, in Chinese, a personal noun with a plural suffix 们 can not be modified by a definite numeral-measure word. Thus the above sentence must drop either 们 or 三个.