a offense for a small 5th grade boys team

Whenever I here someone with similiar problems to yours, I always come back to this simple offense, the 1-4 with the posts up at the elbows. Normally, this is for teams with weak posts and strong cutting wings, but in your case it sounds like it will do the trick. Also, make sure your wings are free throw line extended. This will help with base line cuts if they are in a true 2-3 zone. If they go with a 2-1-2, then you should be set. You basically set up the offense with a good driving PG, not neccessarily to shoot, but to suck the defense in. Then, kick it out to the wings, let them shoot. This will eventually, draw the bottom two blocks out, then the high posts should be open, make sure they know it's alright to shoot. It's basically an offense with good outside shooting. The high posts should run some motion in and out with the wings to really get the defense confused. The rebounding situation in this offense is also good for a small team, since they are normally longer rebounds from the outside shooting and should give your smaller players a chance to get more boards. Just be sure to have someone ready for the defensive release.
That's all I can think of for now.