Have seen with 〜た＋ことがある

Grammar Explanation: Previous experience with 〜た＋ことがある

Sacchan and her friends come across a torn piece of paper with 「あたり１００」 written on it. Thinking it may be for a 100,000 yen prize, the girls head to the shopping district to redeem it. Along the way, their friend Nonoko says she doesn’t recognize where the ticket is from, but Sacchan’s mother says it looks familiar somehow. Kotoha admits it seemed familiar to her as well, but she thought it was just her imagination until now.

結衣(ゆい):: 「私(わたし)とさっちゃんとののちゃんは知(し)らなくて」; “Even though Sacchan, Nono-chan, and I don't know it...”
さっちゃん:: 「かーちゃんと琴(こと)ちゃんは見(み)たことがある」; “My mom and Koto-chan have seen it before.”; Literal: “Mom and Koto-chan have a thing where they saw it.”

Key Points

1見たことがある means prior experience

見(み)たことがある says Sacchan’s mom and Kotoha have seen the ticket or something like it before.
The pattern does not say they are seeing it now; it points to memory.

2かーちゃん is a casual label

かーちゃん is a childlike way to say mom.

ちゃん is an affectionate, informal suffix attached to names, used mainly for children, close friends, and family members.