Re: Lost toy at sitter's house, advice?
I don't let my kids take "special" toys anywhere for this reason. Kids lose track of things (heck, *I* lose track of things)...
Special toys stay at home. PERIOD.
Chalk it up to a loss and replace the train. The next time he wants to take it somewhere, tell him "No, remember the last time we took it somewhere it got lost and you didn't have it for several days?"
Look in the stores, look on Ebay, put an add on craigslist, etc...