the pinyin of 朋友 and 小朋友
Why is the pinyin of 朋友 different from the pinyin of 小朋友？
The hanyu pinyins of 朋友 should be peng(2) you (0), 友 being read as the soft sound (轻声)；
On page 7 of the textbook, you would have seen the phrase “小朋友”，with 友 being read as the third sound (第三声）.
So, why the inconsistency? The reason being, when we are referring to “朋友”, we are referring to the phrase as "friends". However, when we say "小朋友", we are referring to children/ kids, a specific term with totally different meaning to "friends", hence "小朋友" is read as xiao (3) peng(2) you (3) , “友” being of the third sound.