There are a couple of different things you could have your players do at the beginning of practice. For kids U14 and below as they show up have them start small-sided games. When you show up set up a small field; as soon as the first two kids show up have them play 1v1. As kids come add them to the game up to 3v3 or 4v4. Once there is a 3v3 or 4v4 game going have additional kids that come start up another small-sided game. Kids love to play soccer so why not let them do it? It is important though to just let the kids play, there should be NO COACHING. You may start to notice that kids will want to come to practice earlier and earlier because they know they will get to play and have fun. Another benefit of this is that when you decide you want to start practice the kids should already be partially warmed up and mentally prepared to play soccer.
Older children may not be able to show up to practice and just play without risking injury. Those children should be encouraged to pass the ball (preferably while moving) or juggle the ball.