In field Fly Rule

[mrcaroll]

I was doing a major girls ( 12-14)softball game last night. Runners on 1st and 2nd 1 out. Fly ball to second baseman. I called infield fly when the ball reached its pinnacle. Runner continued to first and told the runner on first to go. The second baseman never caught the ball and the runner from second went to third. I made the mistake of calling a dead ball when i seen the girl who hit the ball round first going to second. I then called her out and sent the runners back to there original bases. The coached questioned my call about the infield fly rule. He said the girl was not able to catch the ball. I said it is not my position to determine the skill level of a player, just the position of the ball in the infield and if it was a catchable. He then said his runners should be allowed to advance on this rule. I agreed but said i had called the play dead, so they must return. I know i made the mistake on the dead ball. What should i have done with the girl who continued to run? and where should the runners on first and second be placed.