Navigating the site letsgofestas.com.br in some situations an error occurs in IE:
https://i.stack.imgur.com/Cr11k.png

I can not trace the reason for the error.
There follows a pattern, while the user navigates in some given time the error occurs. Do not have a specific page or specific code….
I was able to get the site to crash IE twice – though I suspect it may be that IE is killing itself on account of how much memory is being used on the site. It died both times at about 85mb of memory usage. This leads me to suspect that you have some scripting issues that are eating up the memory.
While I cannot tell you specifics with regards to what scripting needs to be revisited, and perhaps re-considered, I did focus on the Infantil and Adulto pages in gaining the memory growth necessary for both crashes.
You might consider taking some of your JavaScript over to Code Review and see if there are any optimizations that can be made which would result in better memory-management in IE7. I was unable to get the site to crash in IE10.