Help is a catenative verb. That means other verbs can follow it. For help, these following verbs can be the bare infinitive or the to-infinitive. Sometimes there is an object between the two if the subject of the infinitive is different than the subject of "help."
Father helps me (to)do my homework. Fluoride in drinking water helps (to)prevent too
Actually, the following is also correct: "You are among the 200 extra staff recruited to help to look after them." However, the second "to" is usually dropped for the sake of brevity. Note that the following are also correct:
You are among the 200 extra staff recruited to help with looking after them.
You are among the 200 extra staff recruited for helping to look after them.