You perfectly analyzed this photo - I guess it's also because you took it in a way that will amplify the desire message and effect - there is nothing to add in that aspect.

I would take a guess that in your other photo the bear does look sad but also accepting - as you mentioned in your post, we grow and we change and develop ourselves into something more whole and complicated, so it might be nostalgic and a little sad - but we do have to keep the past behind and concentrate on the present and on the future - dwelling in the past might blind us from looking at the present clearly.
If you will look - the teddy bear hand's looks like he is catching the upper part of the garbage bin and closes it on himself in acceptance of the fact that his time is over and the present belongs to others.

All the same - we should still keep our past memories and our childish behavior - when we will have our own children - it will come handy! so maybe the bear should be kept in the garage, until the time comes he is needed again :)