Answer:
Don't they?
Step-by-step explanation:
A question can be defined as a statement that begs or requires an answer, response or reply from a respondent.
A question tag can be defined as a very short clause placed at the end of a sentence (statement) which changes it to a question. Some examples of tags used in English language are: can we, can't we, should I, aren't they, shouldn't they, wouldn't it, weren't they, do I, shall we, etc.
In this scenario, the question tag to use in completing the phrase is "don't they?" because it creates a balance with the subject which is in plural form.
Hence, using the question tag we have;
All children like sweets, don't they?