I was wondering if there are limits on the amount of times a movie can be watched on Amazon. My kids have been enjoying Willie Wonka and the Chocolate Factory over the last few weeks for free, but when we went to watch it this morning it wanted to charge us for the privilege.

It looks like it has been taken off Prime and you have to rent or buy.

they only have stuff available for a short while then you have to either buy or rent , I cancelled my Amazon prime and stuck to netflix

As with all subscription streaming services the rights are only for certain length of time (usually a year). Once the rights expire they either have to remove it or negotiate new rights.

The difference with Amazon over Netflix is they also have a rental/purchase service so when the rights expire for subscription streaming they can still offer rental/purchase options. As rental/purchase sales provide a higher profit margin anyone who agrees to the basic payment structure can get these rights but with subscription streaming the best money is made when rights holders sell the content on an exclusive basis and even none exclusive rights have a more complex payment structure that needs negotiated so its a lot tougher to get the rights sorted (and a common practice for something that's popular on a service is to refuse to negotiate until after the rights expire knowing customers will put pressure on the service to pay over the odds)