I will start with a short recap of what parties are like in Mexico, of course there are different factors in place, but normally, they don't last less than 4 hours. If the parents have rented a party place, it usualy goes for that amount of time, however, it is very common for the closest guests to go to the parent's house afterwards to continue the celebration. If the party takes place at a house, it can last for hours and hours. It is also common to have alcohol for adults, so it can become an adult party that can sometimes end far beyond kids bedtime.
I guess that is why I was so surprised when I heard that parties here were just two hours long. Even though I think we Mexicans exagerate this whole celebration thing, I don't think 2 hours is enough for all the anticipation a birthday party generates in a child. I know it is a lot of work for the parents (mostly if kids are just dropped of and then picked up) but it is just once a year and I believe it's worth it.
Furthermore, if Mom and Dad see it as a good opportunity to spend some time together while their kid is at a party, I definitely have to say that 2 hours is not enough!
If I take this 2-hour culture a bit further, I think, in general, parties and reunions here in Canada are just that long... for instance, I was invited to a cookie swap that will last for 2 hours; I invited some friends for lunch the other day and they only stayed for 2 hours... holiday parties, company get-togethers... 2 hours! When you have lived in a place in which time is not an issue when you are having fun, it is very hard to keep an eye on your watch!