Teaching your players how to slide in baseball is a pretty easy thing, what kid doesn't like getting dirty? Teaching them the proper wat to slide which is both safe and smart takes a bit more work. What follows are some tips picked up over years of playing and coaching that should help make the experience fun and productive, if it's fun afterall the odds of kids actually wanting to hone the skill are far greater.
While the headfirst slide is popular and it looks good as the pros mostly do this, kids want to emulate it, however the first skill in sliding is learning the hook slide. The hook slide is the one in which you slide in feet first using your buttocks to take the brunt of the impact. All that flesh has to be useful for something right? The problem with many kids using the hook slide is that at first they tend to want to flop straight down on their backside at first which has an effect akin to planting them in place rather than sliding. So how do you teach them the right way?
Get a pair of soft bases, not the more solid "Hollywood bases" which are firm and stationary. Pace off the 60 or 90 feet depending on the age level you are teaching in the outfield and place the bases that distance apart from each other. have the kids one at a time take off from bag "A' to bag "B" and excute a hook slide. The outfield grass is less abrassive so it's great for this unless of course you are the one that has to get grass stains out of their clothes. What this does is it number one gets kids used to sliding, number two it helps them learn how to gauge where to begin their slide so they dont' start too earl or late. Too early a slide and they won't make the base, too late and they can get injured hence the soft moveable bases. That keeps anyone from getting jammed on too hard of a slide executed too late.
Once they have a good grasp on executing the hook slide place fielders on the bases and have them throw the ball to each other when the runner is advancing. This gives the runner a chance to get used to the idea of people being at the base and the ball being in the air near them. This helps keep kids from getting gun shy around a throw coming towards them so they slide rather than duck or run in another direction. If you've coached little kids (Eight and under) you've probably seen this happen. If you break the habit early all the better. Once that is done move them to the infiield and the process is complete. To keep it interesting play pickel or hot box as it is called in some places to further reinforce the kids getting used to sliding and keep it fun.
When kids reach around age ten it is about the right time to teach the head first slide, especially to your faster runners that will likely make stolen base attempts. Again train in the outfield initially which is softer. It is good to get the kids used to doing two things, one is sliding for the outside of the base (Situation dependant slidng techniques can be taught at a later age and are usually picked up by better base runners on instinct) and two get the kids used to keeping there hands balled in a fist. To do this have them hold a batting glove in each hand or what we do is use a small piece of foam used on the hand grips of walking crutches. This prevents the runner from jamming or breaking a finger when sliding into the base and lessens the chance or severity of injury should their hand be stepped on.
Most important of all is that you teach when each slide is appropriate. Strongly discourage kids before Babe Ruth league ages from ever sliding head first into home. Remember this is a game and even a young catcher still has hard equipment on and can be a heck of an immovable force at the plate. Too many injuries occur with kids trying head first slides at the plate. Teach them when it is appropriate to slide head first and hook style at second and third as well. A head first slide is used when there is no force play most commonly, ie; a stolen base attempt, whereas a hook slide is used in the case of a force play such as a double play situation. Take out slides shouldn't be taught until players are older.
Especially with young kids keep the learning process fun. Institute a rewards system to encourage them to learn and use the proper sliding techniques. Most kids will need very little help, some will be a project to teach. keep it safe and keep it fun, learning doesn't have to be a chore and it doesn't have to feel like a drill.