Using some of the reference you gave created a modern-retro baseball log. Kind of the way the O's logo has evolved, but still appropriate for the age group. Please give comments if this direction suits you.
Hey CT... can you color the bat dark green on #13. The logo will be on the front of the players hats and will be raised embroidery, so we have to limit the colors. Thanks for your efforts. You're design is getting lots of attention with the players.