Boy whose "imaginary" friend turns out to be his neighbor.

[mab500]

A mother and son move into a new house, the boy tells the mother he has a new friend, she thinks he's imaginary. She finds out in the end it's the neighbor and there is a tunnel leading from the boys closet to the neighbors house.

I have no idea what movie this is. I saw it in the 90s....

[JayJayM12]

This might be too recent (you said you saw it in the 90s), but this sounds EXACTLY like "Someone is Watching" from 2000:  http://www.imdb.com/title/tt0203929/