If I may ask two questions:
Is 子 necessary in this sentence?
Sometimes the pronunciation of 孩 when referring to female (using google, such as 一个女孩) has an "r" sound at the end. Is this common or is it localized somewhere?
I've started watching a few people on youtube, so it's helping with a few questions (now I know what all the little lines mean for pronunciation, but I'm still a long way off from doing it properly), but I haven't gotten to something that explains these yet.
• "子" is not necessary, in this case, you can just simply cut it out. But when you use a word with a "子" and another Chinese character (e.g. 杯子 (bēi zi, cup), 椅子 (yǐ zi, chair) ), you'd better keep the character "子" , since it's important for understanding the object you want to describe. Without the character "子", it's hard for us to tell if it is the object or the other objects which sounded the same, especially in conversation.
• Actually, that "r" sound is the character "儿". It has no actual meaning. It can be added to the end of some words, and it is not used only with female (e.g. 男孩儿, boy). It's very common in China, especially in the north.
For question 1 子 is not necessary in the word 男孩(boy) or 女孩(girl). It's ok to add it in, but we don't use 男孩子 or 女孩子 very often in Taiwan now.
By the way, 子 always appear in some nons. 孩子(kid), 車子(car), 鞋子(shoes), 褲子(pant), etc.
For question 2 We don't pronounce "r" sound at the end of the word 女孩 in Taiwan. Only in some situations we want to say it in a cute way, we'll say 女孩兒.
Just provide some opinions about it. Hope these answers could help you.