Certain verbs are followed by an object and the infinitive without to. They are: let, make, see, hear, watch, notice, help (in an informal style), and (in a few constructions) have and know.
She lets her children stay up very late.
I made them give me the money back.
I didn't see you come in.
I heard her say that she was fed up.
Did you feel the earth move?
Could you help me unload the car?
Have Mrs. Hansen come in, please.
I've never known him (to) pay for a drink.

When these verbs are used in the passive, they are followed by the to-infinitive.
He was made to pay back the money.
She was heard to say that she disagreed.

Label: hear etc., Let, make