Soccer player field/bench time calculation

I've been trying different formulas and matching players to in/out sub time, but I can't get anything to work.

What I am trying to do is for a given soccer game (my kid's team), is to calculate the actual playing time for each player. The coach is trying to make sure everyone gets the right amount of time, keep parents happy, etc.

I know some absolutes: Match is divided into 2 halves, each is 25 minutes long. We know who starts each game, and in/out subs during the half and what minute during the half they subbed on/off. What we want to calculate is for each child on the roster how much playing time and bench time per game by half. The position is not important at this point. Anyone game enough to help me reach my "goal". I know pretty bad pun, but I couldn't resist. Thanks in advance.