I heard the expression such as "He objected to being treated like a small boy". Can I instead say "He objected to be treated like a small boy"?
The word “to” functions as a preposition in “objected to” which is a phrasal verb. Use a gerund (“being” in this case) instead of an infinitive (“to be treated”) as the object of the preposition “to”. You cannot say: "He objected to be treated like a small boy." Other examples are “committed to changing (*change)” and “looking forward to being pampered (*be pampered)”.