Theoretically, it is Ok for 5 years old kids see 3D movies. However, being an adult, you may also feel uncomfortable after seeing 3D movies for too long. I believe you have such experience that when you watch too long 3D movies, your eyes feel strain or dry, even shed tears, and headache. 3D movies required the eyes to converge in front or beyond the screen. So parents you had better pay attentions to your kid's reaction. I suggest that watching 3D movies do not exceed one hour and have a rest. Second, when watching 3D movies, trying to sit at a distance from the screen, not too close.