The U.S. Open isn’t just for grown-ups.At this annual pretournament celebration at the United States Tennis Association Billie Jean King National Tennis Center, children can get into the swing of things with a festival of tennis clinics and athletic activities.The highlights include Little Tennis, at which preschoolers can hit small balls, and Beat the Pro, a chance for older children to compete against players from the Open.The day continues with a stadium show of tennis and entertainment, including live music by Demi Lovato, Colby O’Donis and Menudo.
Menudo and host, Susie Castillo, pose before the big performance at Arthur Ashe Kids' Day.
Many stars including Ugly Betty's Mark Indelicato are at the event.
Lindsay Davenport, Rodger Federer, Serena Williams and Rafael Nadal make an appearance at the event.
Nadal and Federer have a laugh as spectators with participants of Arthur Ashe Kids' Day.
James Blake looking good at the Arthur Ashe Kids' Day.
Ana Ivanovic with United States Olympic swimming gold medalist Cullen Jones before the start of Arthur Ashe Kids' Day.
Unseeded Caroline Wozniacki won the women’s Pilot Pen title, her second career victory, beating top-seeded Anna Chakvetadze 3-6, 6-4, 6-1.
She won her first WTA Tour win in Stockholm, then reached the third round at the Olympics, where she lost to eventual gold-medalist Elena Dementieva. “Stockholm was in Scandinavia, it was my first tournament and it was smaller than this,” she said. “Here, it’s the tournament before the U.S. Open, and it’s a really big tournament. You know, I have beaten some really great players on my way to win this tournament.”
Wozniacki has moved up from No. 64 in January to No. 22, and is expected to break into the top 20 for the first time.
The teenager still has a year of high school left, and said until recently, she considered her biggest tennis achievement beating her older brother.
In the men's singles, Marin Cilic, world ranked no. 31, won his first ATP Tour event in front of the American crowd, beating local Mardy Fish 6-4, 4-6, 6-2.
The 19-year-old Croat, seeded sixth, made a tough stand all week to emerge as a possible threat at the US Open, the last Grand Slam of the year, which starts next Monday in New York."I'm unbelievably excited," Cilic said. "I was a little bit nervous in the beginning of the third set. I got my rhythm back. I was really pumped up when I had to be. Really enjoyed the moment in the end."
The 6-foot-6 Croat has now compiled a 31-21 on the season (18-12 on hard courts). He is the second Croat after Ivo Karlovic to capture an ATP title this season.
(Images by Elsa/Getty Images)
Here are more pictures from parties before the U.S. Open. The U.S. Open Wilson Party were taken place at Mansion, New York. Some of the players seen at the party are Roger Federer, Serena Williams, Venus Williams, Novak Djokovic and Jonas Bjorkman.
The U.S. Open isn’t just for grown-ups.
Menudo and host, Susie Castillo, pose before the big performance at Arthur Ashe Kids' Day.
Many stars including Ugly Betty's Mark Indelicato are at the event.
Lindsay Davenport, Rodger Federer, Serena Williams and Rafael Nadal make an appearance at the event.
Nadal and Federer have a laugh as spectators with participants of Arthur Ashe Kids' Day.
James Blake looking good at the Arthur Ashe Kids' Day.
Ana Ivanovic with United States Olympic swimming gold medalist Cullen Jones before the start of Arthur Ashe Kids' Day.
Unseeded Caroline Wozniacki won the women’s Pilot Pen title, her second career victory, beating top-seeded Anna Chakvetadze 3-6, 6-4, 6-1. 
In the men's singles, Marin Cilic, world ranked no. 31, won his first ATP Tour event in front of the American crowd, beating local Mardy Fish 6-4, 4-6, 6-2.