I also left mine with the parents. But I had a 40 gal breeder solely for my BN colony.
I fed them NLS Grow and they ate whatever the parents ate, zuchinni, cucumber, sweet bell pepper strips, mango, papaya, mushrooms, romaine lettuce.
A few times a week i fed the tank defrosted frozen Hikari, bloodworms, spirulina shrimp, tubifex etc. And also the Hikari algae wafers and Omega one veggie rounds.
The babies could shred a piece of romaine lettuce in no time!!