From what I remember a young boy is in a van with a comic or coloring book. His sister and parents are in a field looking at what I believe was a injured rabbit, suddenly a monster grabs the boy out of the van and takes off in the woods. The father chases after the monster in the woods and can't find his son only hearing his son scream for help. At the end of the movie the parents battle the monster and it gets trapped underground before the credits the monster's hand pops out of the ground and roars. From what I can remember I believe the monster had scales that were a greenish color and walked like a human if it helps I know the movie was made before the year 2000 and was probably from the 70s or 80s

Rawhead Rex (1986)

Wikipedia synopsis excerpt:
On the road, Howard's daughter needs to go to the bathroom, so Howard pulls over and lets her go by a tree. Hearing her suddenly scream, Howard and his wife rush to her; Howard's son stays in the van, alone. Rawhead kills Howard's son and takes the body into the woods. Infuriated by the police's unsuccessful efforts to track down Rawhead, Howard returns to the church. He discovers that there is a weapon shown in the stained glass window that can be used to defeat the monster.

http://en.wikipedia.org/wiki/Rawhead_Rex_(film)