First off, i don't agree with the bad parent comments, but I do however agree that this whole thread is a bit mixed up.
Ok so first off, the ids shoe gets caught... very traumatic for the kid, although it happened to me at that age (not a WDW) and i can't remember a thing about it.
Secondly, a very kind and shocked CM, who is probably just as shook up as the parent offers FREE money to buy replacement temporary shoes. Very good cast member in my opinion.
Next, the coupon/voucher thing isn't enough to cover the full cost of a pair of flip-flops/shoes that you could find. Why not go to guest services and
ask if they have any kids shoes avaliable in the park for $25 or less, if not what arer the cheapest shoes they offer.
Ok, so lets say crocs are the cheapest, at lets say $35 (no idea of actually pricing in the parks), the kid will probably like the choice of colours availiable, and lets be honest... at 4 i was totally dressed by my parents, i wore HIDEOUS stuff, but only because i was fashion aware, as about 99% of kids arn't.
Now the crocs might choose to be the best pair of shoes the kid has ever worn, never wants to take them off, alternativley, they wear them for the day, then never touch them again. Thats not the end of the world, sell them on ebay when you get home, or give them to another child that you know.
I don't think trying to buy a plushy is the best way to go though, ok the kid will have cried for a bit, but kids that age are pretty resiliant (sp?), they fall over scrape their knee then run straight off, by the end of the day they were probably fine, only problem occurs when the parents remind the kids constantly of what happened "are you ok, honey? did the nasty stairs try to eat your shoes?"
Back to the point, the kid will not have needed a plushy, and you had $25 of FREE disney money to spend on shoes, so if you're not going to use it, give it too a family whos kids might have lost their shoes (fallen off while in stroller for exmple)
Although it is something you as a parent will find it had to forget, theres no point loosing sleep over it, your kiddy is fine. You're very fortunate.
Ok rant over, hope that didn't come across as too harsh
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