A mother is scolding her daughter. The uncle (Tomozou) speaks first:
「おかあさん、お歳暮の広告見ちゃダメ？」
友蔵が頼んでもおかあさんは首を縦に振らなかった。
「ダメですっ。」"Mother, is looking at year-end adverts not allowed?"
Even though it was Tomozou who asked, mother didn't nod in agreement.
"It's not allowed."
(my TL attempt)
My main question is what is the meaning of ちゃ (in bold). If I were to say this I would write something like お歳暮の広告を見るのはダメ。So my first thought was that ちゃ could be a contraction of のは but that doesn't sound likely.
My secondary question (possibly related) is why does it say that the mother didn't nod in agreement? I guess this is something to do with how you answer negative questions in Japanese, but even then it seems like a strange thing to say.
