updated 04/09/2012 AT 2:50 PM ET
•originally published 04/09/2012 AT 8:00 AM ET
“Jennifer had planned a fun day to celebrate Casper’s birthday,” a source tells PEOPLE. And the day began with a four-wheeled birthday present: a customized white Dodge Ram truck.
Lopez “knew that Casper really wanted a truck, and Casper was very excited about the generous gift,” says the source.
Lopez also Tweeted: “@BEAUcasperSMART ‘Beau has a birthday we’re so glad we hope it[’]s the happiest Birthday Beau ever has!’ #singingtweet. HAPPY BIRTHDAY BEAR!!!”