Many Sunday morning Sunday Schools see participation numbers drop considerably in the summer months. Understandable due to sports, summer vacations, and just a lovely summer day at the lake.
I would encourage you to focus on simple child/family events that are one-time special events on a weeknight or Sunday evening. The scheduled event time is for you to connect with children and, hopefully, their parents. The event should be more fun than a lesson.
You could make them grade specific or an all-ages welcome. You will have to determine that by the type of event you plan. I would count an event successful if you had at least 3 to 5 families attend. It shouldn't be a big blowout event. It should be a casual drop-in and enjoy a visit kind of opportunity. If you tend to have the same families continue attending, challenge them to invite friends to the next event.
Example of easy Connections:
Popsicles in the park.
Mid-week story-time for preschoolers.
Families that stretch together play together in Yoga class!
Create a sizeable visual worship art for a church service.
Bikes and trikes in the church parking lot or gym.
Chalk a greeting for those who come to the church door.
Food truck Fun with the tweens.
Chocolate Chip Cookie Ice Cream Sandwich Night
You will find yourself ministering to families in such simple ways over the summer. It will help your relationships grow so that when they get an email or text from you that you can't wait to see them for Fall Sunday School programming, they believe you!