At 10U you will need to partner with and or poach from the local Rec teams. I know that doesn't sound like a nice thing to do but you will need to get in front of kids who are interested in softball. You could offer your local rec org to hold a winter camp for 10U and under kids. Have the girls on your team help or at least take part in the camp. The parents may ask you for more details. Most kids at 10U are coming from Rec teams and are just getting interested in travel. Also the not so fun part of the process is marketing your team. You need to be heavy on socials and softball boards around your area. Most importantly make sure your team is sound fundamentally and wins. That more than anything will attract kids and parents during tournaments.