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"
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.
Reporting by PERNILLA CEDENHEIM