Please see READY/SET/GO on the navigation bar "Goal keeping in General," to start understanding one of the basics.
Our U8 goalkeepers are not expected to be spectacular goal savers. The reason U8 goal keeping is used, is to introduce them slowly to the concept. Things coaches should concentrate on is proper handling of the ball, distribution after reception or possession, protecting the face and smothering the ball. No diving should be taught at this level.
Keepers should not have knee or elbow pads, as they should never land on these areas hard. Soft landing should be taught. Keepers must have a different color jersey (target jersey is fine) than either team and one keeper MUST be designated, even if you choose to use him/her as a regular player.
At the U8 level, you might want to look at your keeper as the player who used to be the "defensive" player and stood by your goal. Don't be afraid to instruct your keeper to come out of the box when needed to kick the ball defensively if necessary. Teach him/her the basics of "no passback/handling," and not reaching over the penalty box when distributing (that is considered a handball).
Keepers here may not punt a ball out of their area and there are no penalty shots on goal. Distribution of the ball is done by delivering the ball to a team mate by a throw or roll.
Don't have just one keeper in goal at the U8 level. I suggest you, as minimum, have a different keeper per quarter if you can find players willing to play the position.