Tag questions (short answer) in declarative sentences:
A tag is formed by taking the helping verb of the main verb (make it a question to find the helping verb).
Everybody forgot to congratulate her.
Did everybody forget to congratulate her?
TAG: Everybody forgot to congratulate her, didn't they?
Main verb: forget Tense: simple past (forgot).
Also, don't forget that in a declarative sentence tag, the tag must be negative interrogative (didn't they?). In a negative sentence, the tag must be plain interrogative (They didn't forget to congratulate her, did they?).
You can practice with these:
The boys have found the dog and brought him home. [tricky, kind of]
You will be going to school this afternoon.
We wouldn't have been in town so late, normally.
Clues: the helping verbs are either in the sentence (have, will, is/are, would/should) but in the present and simple past, you have to come up with [do/does and did).
You speak Russian, don't you? You have to remember that do is the helping verb.
This is just a basic introduction, not the whole entire story.
Here is an important irregularity:
I'm being clear, aren't I? :) [regular]
VERSUS I'm being clear, am I? [in response to praise or to be sarcastic, for example]
That one does not follow the rules, you just have to learn it. First person sentence in the present tense with a tag.
Also, in a negative sentence: I'm not being clear, am I?
Best Answer
Everybody will understand if you say:
there's nothing grammatically wrong with it, but it is not usual to have two auxiliaries in this sort of tags. And I would advise you strongly not to use it in an EFL exam.
The tag is built with the auxiliary that has the most influence on the meaning of the sentence. In your example have is the auxiliary that helps build the present perfect tense, it only modifies "scold (the child)".
Should is a modal auxiliary, it helps expressing the speaker's opinion towards the action that follows (in your sentence reproach towards "you"). It influences the whole group: present perfect verb ("have scolded") plus object ("the child"). The modal takes precedence over the tense auxiliary.
Other examples:
Your next question might be: what about if we have two modals, in the same verb group? Well, that is grammatically impossible in English. When two different modalities have to be expressed, one of the modal verbs is replaced by a lexical verb.
Let's say we want to express the idea of advice (indicated in English by modal "should") together with ability (expressed by modal "can"). In that case we substitute the modality usually expressed by "can" by a lexical verbal that conveys the same idea: