PARENTING : Fitness for Youngsters : * Regular exercise is vital for the good physical and mental health of children.

Even in sunny Southern California, the weather outside can be frightful.

And with those some times rainy winter months still ahead, parents will need to find ways to keep kids busy when they’re stuck inside and whining, “I’m BORRRED!” and bouncing off the walls. Or worse, when they are vegging in front of the TV.

There is another option. Kids can expend their energy and keep fit (and you can stay sane) even during the worst weather. Several Valley gyms cater to children, offering everything from basketball to ballet. Kids can learn modern, jazz, hip-hop and tap dances; practice cheerleading, gymnastics and aerobics; master judo and karate; swim laps; or play with Frisbees, jump ropes or on trampolines.

And since it’s all indoors, they’ll stay warm and dry while they work out (unless they’re in the pool, that is).

“Kids need to move around,” said Karen Lynn O’Brien, wellness director of the Mid-Valley YMCA in Van Nuys and mother of 5-year-old triplets. “Especially now that a lot of schools are cutting out PE, this is where children learn to take care of their bodies. I take my triplets here and have them do everything.”

During inclement weather, Calabasas parent Penny Erickson, a pediatric occupational therapist, encourages daughter Lindsay, 4, to jump rope in the house and play on an indoor hopscotch mat. She has also enrolled her child in a local gym.

“Lindsay had all this endless energy that wasn’t being focused,” Erickson said. “But since joining the gym, she learned to focus and work as a team player. She’s developed self-confidence, and she feels good about what she is doing. And when she gets her exercise, she sleeps better at night.”

But little Lindsay is in the minority when it comes to working out. Studies show that most youngsters do not get enough exercise. Less than half of the nation’s children participate in 20 minutes of vigorous activity three times a week--the minimum required to maintain adequate fitness.

Year-round physical exertion is important, even for very young children, according to Encino pediatrician Pejman Salimpour. “The sooner children get started with physical activity, the better,” he said. “People who are active are more energetic, full of life and happier, and there are health risks in having a sedentary lifestyle.”

Benefits of exercise extend beyond the playing court to the classroom and home, said preschool gymnastics specialist Connie Thornbury, an instructor at Junior Elite Training Center in Woodland Hills.

But Salimpour cautions parents: “Young children should do what they are physically capable of doing, but they should not be pushed into it because they will resent it, they will learn to hate physical activity and exercises.”

WHERE KIDS CAN WORK OUT

Here is a sampling of Valley gyms that cater to kids.

Fun & Fit, 1919 W. Burbank Blvd., Burbank; (818) 845-0700; and 21021 Soledad Canyon, Canyon Country; (805) 255-7244. Gymnastics. (Dance classes also offered at Burbank location.) Ages 12 months and up. $76-$106 for eight weeks, plus $30 annual registration.

Junior Elite Training Center, 6708 Variel Ave., Canoga Park; (818) 716-5382. Gymnastics, ballet, tap, jazz, hip hop. Ages 18 months and older. $30-$80 a month, plus annual $50 membership.

Junior Gym, 14720 Oxnard St., Van Nuys; (818) 785-2177. Gymnastics, soccer, judo. Ages 15 months to 12 years. $99 for eight weeks, plus $25 annual registration. Discounts for more than one child per family; discounts for enrolling in more than one class.

Le Club Gymnastics, 19555 Prairie St., Northridge; (818) 886-3331. Gymnastics, cheerleading, modern dance, karate. Ages 18 months and older. $49-69 per month. Special Olympics for children with special needs, ages 8 and older, held Monday evenings. Free.

Li Ning’s, 9700 Topanga Canyon Blvd., Chatsworth; (818) 727-9222. Gymnastics, ballet, jazz, hip hop, tap, fencing, aerobics, cheerleading. Ages 2 to adult. $30-$80 a month.

Mid-Valley YMCA; 6901 Lennox Ave., Van Nuys; (818) 989-3800. Swimming, basketball, ballet, gymnastics, weight training, karate. Ages 3 months to adult. $25 to $45 per month. Discounts for members.

My Gym; 22289 Mulholland Highway, Woodland Hills (818) 222-6496. Also at 17651 Vanowen St., Van Nuys, (818) 996-8725. Relay races, gymnastic tumbling, free play, introductory sports, Frisbees, stilts, tight ropes, jump ropes. Ages 3 months to 8 years. $95 for eight weeks.

West Valley Family YMCA, 18810 Vanowen St., Reseda; (818) 345-7393. Karate, ballet, aerobics, hip-hop dancing, swimming. Ages 3 months and older. $28 to $50 per month. Discounts for members.