"I can't believe my boys are getting so big!" she Tweets about 5-year-old Preston and 4-year-old Jayden
Credit: Flynet

From a hamburger run to the Happiest Place on Earth, Britney Spears had her hands full over the weekend while marking her sons’ latest milestones.

The pop star, 28, treated Jayden, who turned 4 on Sunday, to Johnny Rockets in Calabasas, Calif., and also celebrated son Preston’s fifth birthday.

“Spent the boys’ bday weekend at Disney and had a blast,” Spears Tweeted Tuesday. “I can’t believe my boys are getting so big! Happy birthday JJ and Preston. – Brit”

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The brothers, a source tells PEOPLE, “went wild” at the theme park in Anaheim, Calif., on Saturday before having a small bash at home.

Also on the agenda for the birthday boys? Having yet another party. “The boys also brought a cake to school and celebrated with their friends,” says the source.