What movie features aliens masquerading as humans with inverted knee caps?

The movie is about aliens repopulating Earth with themselves, secretly, by disguising themselves as humans. When they reveal themselves, their kneecaps invert and I think their arms fold out even longer.

One of the characters is a black boy about 12-years-old, who lives next door to the protagonist. He's an alien who is spying on the protagonist (I think he was spying).

There was a sequel and the 2 movies were sold as a box set in bargain bins at Walmart, etc.