Missing, Presumed Lost

Although our house isn't that big, we still manage to "lose" quite a few things, mostly courtesy of George. Sometimes things do turn up again, months later, but there are also some which never re-appear (and this is especially the case now that George has discovered the hole in the wall by the handle of the kitchen door - at least two pieces of train track have disappeared inside there). The current list of missing items is:
Wooden Train;
Wooden Carriage;
Train track
one Mitten;
the letter "R" from the little train which spells out his name;
most of George's CDs;
a little magnetic frog from a music box;
half of the pieces from a farm jigsaw;
and the case for the Bagpuss DVD.
I have moved all the furniture and still can't find them, so it is a mystery.