帰ってくる is a compound verb made of 帰る and 来る.
Sometimes the second verb of a compound verb becomes a subsidiary verb and changes its meaning slightly, but it does not in this case.
I think you were confused because these two verbs are both related to "move". I would like to add one more 行く here.
Although 来る and 行く are usually translated to come and go, they are slightly different.
- 来る means "The subject moves toward the speaker's place."
- 行く means "The subject moves away from the speaker's place."
On the other hand, in English, the listener's place matters.
- 帰る means "The subject moves to the place it belongs to."
(Note: "it belongs to" is relative. For example:
出先から会社に帰る。 (from the field to the office),
会社から家に帰る。 (from the office to home))
- 早く帰りなさい (Move to where you belong to.)
- 早く来なさい (Move to where I am.)
- 早く行きなさい (Move away from where I am.)
- 早く帰って来なさい (Move to where you belong to and to where I am.)
- 早く帰って行きなさい (Move to where you belong to and away from where I am.)
早くうちに帰って来なさいよ。and 早くうちに帰りなさいよ。 are almost the same as far as the speaker is at listener's home. Otherwise, the former does not make sense.