My daughter accidentally put a coin through the gear shift opening, and after some clicking noise, it simply disappeared into the unknow place somewhere inside. What harm can it cause? Is it necessary to retieve it before driving it? Or is it OK to drive, as if nothing had happend?
I wouldn’t worry about it.
I’ve removed many center consoles and found coins among other things that dropped thru the gear shift opening and they never caused a problem. I once found a diamond ring. But it didn’t belong to the owner of the vehicle. So it must have dropped in there from the previous owner.
Tester
Now you have a head start on the $ 2.37 that most used cars have in various places.
however…NEVER let her put a coin in the CD slot ! 
Myself I would pursue getting it out. My logic is that just perhaps this prevents gear selection and you are forwarned,why roll the dice? I cant see it costing over a half hour (but that still means a good 50.00 or so) Kids do love putting coins in the CD slot (used to be the casstette slot),and the cig lighter receptacle
thanks guys for all the reply! Now I feel much better. It sounds like it is most likely OK, or even if I have to take it to the repair shop, it woulndn’t be an expensive one. 
I have a 2011 Sienna and I can see how that could happen. With the engine running and your foot on the brake, pull the lever down into drive and then push it to the left to the “S” position. Push down on the lever repeatedly to make sure it will go into ‘4’, "3’, “2”, and “1”. If so, there isn’t a problem.
This is one feature of the Sienna I don’t like. I would prefer a lever on the steering column. This lever coming out of the dashboard reminds me of the 1955 Chrysler products.