Here's the correctly completed dialogue:
Tim: Becky has got a red cap too. Maybe it’s (her cap) 5 **too**. And the neighbours’ twins have got red caps. Maybe it’s one of (their caps) 6 **too**.
Sergey: Try it on, Tim. Does it fit? Hey! It looks great! Now it’s (your cap) 7 **for sure**!
Tim: The wind! Oh, no! Where’s the cap now?
Sergey: Look! It’s up there, in that big tree! So now it’s nobody’s cap...