Hagerstown’s Stephanie Vicarte, 12, solders wires for the toy invention she is working on with her sister Elizabeth, 14, at the museum. (Marylou Tousignant/For The Washington Post)

What makes a toy fun or cool? Nine kids in the Washington region think they know. Their inventions are semifinalists in a toy design contest at the Kid International Discovery Museum in Bethesda, Maryland. The winning design could wind up in stores nationwide!

The museum’s Toy 2.0 Challenge was open to children ages 10 to 18. More than 60 young inventors entered.

Sisters Elizabeth and Stephanie Vicarte of Hagerstown were surprised and thrilled that three of their projects made it into the second round.

Judges included robotics, gaming and space experts. They reviewed each entry for creativity, design and appeal to kids. The semifinalists include spider and hedgehog robots, an electronic treasure hunt game, two kinds of balls, and balloons with changeable faces.

Hyattsville’s Oliver Foley, 12, used modeling clay to create a model of his homing pigeon toy, above, for the Toy 2.0 Challenge at Bethesda’s KID Museum. (Toni L. Sandys/The Washington Post)

Stephanie, 12, was inspired to create a robotic plant after the real turnips and radishes she planted died when she forgot to water them. The battery-powered plant she and her sister designed will “grow” without water, though they might add a sensor to remind kids that real plants need liquid. A second sensor will test whether the temperature is too hot or cold.

The sisters also are working on electronic jewelry that responds to motion and light. Their butterfly pin, for example, will flap its wings.

“We wanted something girls could enjoy,” said Elizabeth, 14. “So we thought, how can we make fashion electronic?”

For the second phase of the contest, each semifinalist is building a model of his or her toy. This model, called a prototype (PRO-toe-type), gives the toymaker an idea of how easy or difficult it would be to make the toy.

Each semifinalist was given a $300 budget for supplies. And they got to spend three hours one-on-one with a mentor who can help them with the trickier parts of their creations, such as attaching LED lights and working motors.

Oliver Foley, 12, of Hyattsville brought a clay model of his robotic pigeon to his first mentoring session.

“It’s kind of like a drone,” he explained, “and you can create mazes the bird can fly through.” Mentor Tim Slagle, a scientist at the museum, talked to Oliver about materials his pigeon could be made from so that it “could survive getting bumped and crashed a few times.”

As the two discussed infrared light beacons and homing devices, Oliver admitted that “this might be a bit harder than I imagined.” But Slagle jumped in. “I can help you make it,” he said. “We can spend our whole next session on building the homing detector circuit.

“I’m constantly thinking of things to make,” Oliver said later, “but this is one of the first things I’ve prototyped. And it’s my first toy invention.”

Ten-year-old Chandler Wimmer of McLean, Virginia, loves robots, too. He and his older brother were on a team that won a national robotics title in 2014. And they created a Web site, www.robotsnow.org, to help elementary schools start robotics programs.

But for the Toy 2.0 Challenge, Chandler focused on his love of games, especially Chinese checkers and Pentago. He designed a 3-D game cube with moving sides and detachable game pieces. The object is to be the first player to move your five game pieces to your opponent’s side.

Rustom Meyer, an engineer and Chandler’s mentor, advised against putting magnets in the game pieces because little kids might swallow them.

“I never really thought about safety when inventing a toy, but I guess you have to,” Chandler said.

He and Meyer decided it would be better to use magnets in the cube itself, to reduce the risk.

Chandler’s game is for age 6 and older. He thought he might have a slight advantage over the other semifinalists “because I’m closer to that age myself, so I know what those kids like to play.”

The other semifinalists are Sebastien Sviatyi, 10, Rockville; Christian Brown, 15, Silver Spring; Alex Fisher, 16, Bethesda; Miranda McMillen, 17, Downingtown, Pennsylvania; and Ben Spector, 17, Herndon.

Prototypes will be shown to the public September 20, and three finalists will be named. This fall, Innovation First International, maker of the popular Hexbug toys, will pick the winning design, which one day could come to a toy store near you.

Tousignant is a freelance writer.

Coming up at the KID Museum

The museum has lots of worshops for age 9 and older, unless otherwise noted.

July 25: “Burn Metal: Soldering.” Learn to solder and then build a light-up memory game you can keep.

July 26: “3-D Design & Print.” Learn the basics of 3-D printing and design using Tinkercad.

August 1: “Coolest Flashlight Ever.” Learn to solder and work with circuits and LEDs while making your own flashlight (ages 7 to 8 can participate with an adult).

August 15: “Raspberry Pi.” Build and race your own robot car.

Kid Museum is at 6400 Democracy Boulevard, Bethesda. Admission is $8. Most workshops have an added fee, which varies. To register or get more information on other fun stuff, have an adult go to kid-museum.org and click on “Events.”