I've noticed that the kids on the better teams are starting to use a "directed" chest ball in place of a header as a way to push the ball to a teammate where they might otherwise have used a header. The problem is that if not done exactly right and the player involves his shoulder and arm in a turning motion, it can be very close to, or can accidentally become, a hand ball. It's also tough to generate the kind of power involved in a head ball, so those chest balls are easily intercepted unless your teammate is very close by.
On the defensive side, lots of high kicks that are quite dangerous. Several times I've seen players on the ground after a boot to the face that was far more dangerous than the header would have been. Fullbacks also attempt to shield a ball that has bounced over them (when they previously would have headed a high bouncing ball), which often results in the defensive player getting run over in a collision or the forward getting tripped by the defender as he runs past. To avoid both of those situations, defenders frequently meet the ball with a foot before it bounces or kick a bouncing ball backwards over their heads. Neither is conducive to possession soccer because it just results in blind booting of the ball.
Corners have been an adventure too. Some teams have worked on plays to keep the ball on the ground, which is good. Some try to hit a near post shot, which is fine but generally ineffective. Others haven't changed anything and the ball just goes over everyone or the ball bounces as kids try various forms of high kicks, chests, and other body parts to put the ball in the net. Goalkeepers have been put in real danger on these types of balls.
So, all in all, it seems like the absence of headers probably has been a wash on the safety front and it has forced some teams to play more possession-oriented soccer, but most have failed if they have even tried at all. It also has inspired some work-arounds (e.g., the directed chest ball or the backwards kick over your head) that aren't really the kinds of things we necessarily want to promote at this age as regular moves.