It is in a sentence said by an old man who is speaking to a group of children.
おめえらはだまっとれ！
I think it should be an imperative form of 「黙る」 but I found, in an online dictionary, that the form is written as 「黙れ」.
Is this word in a form of a certain dialect?
There is another subsidiary verb, おる, in its imperative form.
黙っておる can be contracted to 黙っとる (see this chart).
おる is mainly used to make a humble expression, but it's also used as an arrogant, dialectal or a bit old-fashioned version of simple いる.
お・る〔をる〕【▽居る】
㋑「いる」の古風な、または尊大な言い方。また、「いる」に比べて方言的な響きを帯びる。「君はそこに―・ったのか」「都会にはセミも―・らんようになった」
So it just means "Keep silent!"
The other answers are mainly correct, but they leave out the part that this is usage of 黙っとる or 黙っとれ are still common in certain dialects, mainly western Japan. Some say the dividing line is somewhere between Shizuoka prefecture and Aichi prefecture. Once you go west of Aichi prefecture you hear the とる form a lot, like in phrases as 知っとる (知っている) or やっとる (やっている). Basically, in 標準語 the おる form has been replaced by いる but remains in dialects still.
However, Japanese has a lot of different ways of saying that expression. For example:
黙ってろ
黙っとき
黙っとけ
黙っとりゃあ
黙りなさい
Some of these are dialectical and have slightly different use cases.
