Britney's Birthday Bash for her Boys!

Giant balloons in every imaginable color, homemade ice cream, a vintage popcorn

machine and customized minicars with personalized “license plates”— proud mom Britney Spears went all out in putting together a birthday party to remember for her two precious sons.

Sean Preston, who turned 3 on Sept. 14, and Jayden James, who

turned 2 on Sept. 12, were the guests of honor at the fun soiree held at family

friend Adrienne Maloof-Nassif’s Beverly Hills estate on Sept. 13.

Making the event even more special was the presence of Brit’s little sister, Jamie Lynn, 17, and her 3-month-old daughter, Maddie, who met her cousins for the first time after flying in from Mississippi with Mom on Sept. 10. (Maddie’s dad and Jamie Lynn’s fiance?, Casey Aldridge, 19, stayed at home in Mississippi.)

As for the boys’ friends, “There were some kids there who are Preston’s playmates when he stays with his dad and goes to My Gym,” a source tells OK!. “Jenny McCarthy also brought her  6-year-old son, Evan.”

The lucky kids at the party, including Evan McCarthy and Kingston Rossdale, were treated to toys like Webkins and Skorpies Skates by Kitson Kids, who sponsored the birthday bash. 

Britney, who has looked fantastic in recent months, and stole the show (nabbing three Moonmen including one for Video of the Year) at the 2008 VMAs, enjoyed the party as much as the kids. “She often had Jayden in her arms,” adds the source. “Brit did the  honors when it came time to cut the joint birthday cake, which was decorated with a car, of course.”

The weekend was all about family, and the most special part for the singer was having Jamie Lynn with her. Despite their almost 10-year age difference, the sisters are best friends and talk to each other daily.

“I’m sure Britney would love it if Jamie Lynn were to move to Los Angeles,” the source explains, “but she’s as happy as could be at her home in Mississippi. So the sisters took full advantage of their time together.”

The two will no doubt be back together for Britney’s birthday on Dec. 2. The singer’s next album, Circus, is scheduled to be released on that date, and a party is in the works. The first single from the CD, “Womanizer,” is getting a Sept. 22 release, and at the same time, Britney’s official Web site will be relaunched.

For more about the birthday bash, check out the new issue of OK!, on newsstands everywhere Thursday!

By Mary Ann Norbom