The boy seemed fairly nonthreatening, but Death Eaters could be sneaky. Nevertheless, Tonks was inclined to trust him. That was until he called her 'mum'. Now wait a minute. She might be confused and disoriented, but she definitely wasn't stupid. Or maybe she should have listened to the lady when she was talking. Maybe she mentioned something about a weird time traveling thing where this was the future and she'd be visiting her future child. That seemed strange.
"...no?" she said, clearly unsure of her answer now that she had partially convinced herself that the bun-lady had mentioned time traveling of some sort. Had she? She must have. "I mean... what's your mum's name? I don't think I'm your mum. I don't have any children."