Quarterback Robert Griffin III had major knee surgery in January, but he hopes to be at full speed when the Redskins start training camp next month. (John McDonnell/The Washington Post)

“Be careful.”

That’s what lots of parents tell their kids who play sports. These days, that’s what folks are saying about Washington Nationals star outfielder Bryce Harper and Redskins quarterback Robert Griffin III. Washington sports fans don’t want their favorite players to get hurt again.

Harper injured his knee, shoulder and neck when he ran into an outfield wall May 13. He came back but banged up his knee again when he slid into a base headfirst May 26. Harper has been on the sidelines ever since.

Griffin hurt his knee and missed a game late in the Redskins’ 2012 season. Like Harper, Griffin came back and hurt his knee more seriously in the team’s playoff game against the Seattle Seahawks. Griffin had major knee surgery in January but is talking about going full speed when the Redskins start training camp in July.

Can Harper and Griffin be careful? Almost every sport can be dangerous. That is one of the things that make sports exciting. Baseballs and lacrosse balls are hard, and they fly fast. Anyone who has been hit by a softball knows it isn’t really soft. Bodies bang into one another all the time in football, soccer, basketball and hockey. Injuries happen.

It’s hard to be careful once the game begins. The best players are always hustling and trying to make the impossible play. If Harper and Griffin start to be careful on the field, they might not be the special players we all want them to be.

But athletes, whether they are pros or kids, can be careful before the games begin. How?

First, any athlete should eat well and get plenty of rest. Kids who play sports often get hurt when they are tired. That’s why it’s important that kids don’t play on too many teams or play too many games.

If an athlete does get hurt, he shouldn’t rush back into the action. Everyone wants to play and help the team. But an athlete has to follow doctor’s orders and wait until she is ready to play.

That’s why Washington fans are worried. They are afraid Harper and Griffin will rush back to playing too soon and get hurt again. Athletes who keep getting injured, even ones as talented as Harper and Griffin, do not have careers as long and productive as do athletes who stay healthy.

All athletes, whether superstars in stadiums or kids on a playground, want to play as long as they can. To do that, sometimes they have to be careful.

Fred Bowen will give a talk Saturday at 1 p.m. at the Chevy Chase Library, 8005 Connecticut Ave., Chevy Chase.