No, this is not regarding a workout for preschoolers, but about workouts to do before school starts.  To make the most of fall quarter practices (and to prevent injury) you should start to work on improving core strength over the next month.

The following should take less than 10 minutes.  3 times a week would be good.  If you want to do more feel free.

Lunges - 10 each side
Squats (no weight) - 10
Planks - 30 seconds
Side planks - 30 seconds each side
Situps- 50
Supermen - 2 x 10
Eyes closed balance on one leg - 30s (each leg)

It would also be a great idea to do the knee injury prevention plyos we do at practice (or at least a subset of them).  Enjoy the rest of your summer as much as possible, even though I know you can't wait for practices to start again.  -Alex


PS Here is some further explanation if you need it

Lunges:
    Drop your back knee almost to the ground
    Your front knee should be at 90 degrees, and should NOT GO PAST YOUR ANKLE
    Do them slowly and pay attention to staying balanced.

Squats:
    Feet hip width apart
    Keep your weight on your heels
    Don't let your knee go past your toes (if it does, it probably means your weight is not on your heel)
    Don't round your back
    Squat down slowly until your quads are parallel with the floor

Planks: In pushup position, straight body, but with your elbows on the ground
Side Planks: 90 degrees rotated from planks, one elbow on the ground
Supermen: lay face down, and raise your arms and legs off the ground ... works your back and hamstrings