I would go with a 9 inch or 10 inch glove. Wilson makes a good one:
Wilson 9in Tee-Ball Glove
I got this glove as a present for my friends 4 year old son. It's the perfect size for little hands, but still high quality. Not like the plastic/vinyl gloves you get from the Walmart toy section.
A small size glove
This may vary in the league you play in, but almost all 8U leagues use an 11" softball.
12 inch circumference 12 inch circumference
Your bat should, if you put the end of the barrel on the ground next to you, come up right to where your hip is. That gives you perfect length to cover the plate for inside pitches and outside pitches. 32 inches long would be good for an average 15 year old. 22 ounces would be a good weight for an average 15 year old. A great, informative website gives advice on how to size AND select a Fastpitch Softball Bat. Plus, over 75 bats that cost $100 or more are reviewed and ranked as to the Best Bats for Power Hitters, Slappers, Best Composite Bats, Best Non-Composite Bats, Best Balanced Bats, Best End-loaded Bats and Best Team Bats. www.thecoachreviews.com
The game of softball was invented in Chicago in 1887 by George Hancock. The idea for the ball came from an old boxing glove.