I really like these movies. I have all three of them. I prefer the third one in the series as I think it's the most fun one. It's done in a more goofy way I guess I'd say.
I got the third one first and watched it. I deemed it fine for my son to watch he was 7 or 8 years old at the time. He really enjoyed it. Then I got the first one in the set. I didn't preview it and we just sat down and watched it. In the end scene he says to me, "Dad, why are the beanie's drinking blood?"