not so.
U13 - Playing time not to exceed 25 minutes each way with a size 4 ball. After 50
minutes of playing time, the referee must not allow extra time to be played in
the case of a drawn match in a knock-out competition
50 minutes of playing time, clock on/off for injuries/water-breaks in the normal way. Time expires when ball is dead.
The only thinh that's different is no tie-breaking periods of extra time.