Angelina Jolie and Brad Pitt's kids are growing like weeds -- which is why these shots of them on a shopping trip should make you feel pretty old. 

Angie hit up Fred Segal Thursday afternoon in WeHo with 12-year-old Zahara by her side. The strapping young man carrying the shopping bags is, believe it or not, 13-year-old Pax

Dude was rocking a Playboy hoodie, with matching kicks. Looks like the sibs put a hurting on Mom's credit card ... though we think she can handle it. 

If Angelina's not careful ... someone's gonna offer these kids modeling gigs.