This is out there but could it be one of the Army Men games? Those are the only N64 games I can think of that take place in a kid's room and since you play as little bright green soldiers they could look like lizards (all these years later) if you ever get to drive a jeep.
If you aren't playing as the lizard and it's just something in the room maybe Toy Story 2.
@ CM = Thanks, I must just have logged out too fast.