Is this Obstruction.

My team (7 - 8 yr old coach pitch) had a situation a couple evenings ago which I believe could be ruled as Obstruction but I am unsure. From reading the rules it also leaves me with a doubt.

The situation was that the opposing team's first baseman positioned himself (stood) right in the middle of the first base bag. When my runners approached the base they all slowed down to keep from running over their player.

We had no umpires and were not keeping score. However, in the coming week our tournament starts where the situation would matter.

Any help would be appreciated.

-Al