They learn their first words from Mexican nannies  （主句）   who are often working illegally（定语从句）, just like the maids who scrub floors （maids 的定语从句）and the gardeners who cut the lawns（gardeners 的定语从句）（like...整个词组，是are working 的方式状语）, which help to explain why fixing American's broken immigration system is proving so difficult（why 引导explain 的宾语从句）.（words 的定语从句）

help to do sth.（动宾结构，不定式作宾语）