Just keep signing them up for rec soccer and basketball with their current team. They will eventually want to keep going because their friends are on those teams.
With soccer, kids peel off to go to travel soccer about age 8 and with basketball, its age 10 or so... so kids that stay in rec start to become better as the more skilled players leave.
I'd also put them in track clubs in the spring or winter if possible.
Once the get into video games, iPads, computers and cell phones, it will be hard to get them back outside to play and climb those trees, sadly. So, don't get them that stuff for as long as possible. We've lost all our neighborhood kids to video games by age 11 in my neighborhood. No more outside playing. Consider enrolling in Scouting too if possible.