Can I ask who you would be mad at?
I would be mad in general but also upset with the sitter. Mainly because if she was watching my one child I would suspect she would be playing with him and keeping an eye on him the whole time. There should be by room for "lost toys". This would make me think she wasn't doing a great job watching him. I would also be upset with her not getting back to me. It's not "just a train" as someone else said. It's that child's train which they have make a "bond" with. Children favor certain toys and the sitter should keep looking or AT LEAST reply saying she hasn't found it or offer to buy a new one. I would never let her but a nice sitter would offer. I guess that's just me... I would be overall really distort with the whole situation.