Was this 1930 census from New York City? When I have researched into New York City relatives, I could not believe the number of persons with the same name and birth year. For instance, I found 8 persons named Max Goodman, all born in 1892 to 1893, living in NYC in the early 1900s. It took me a week to confirm which was the correct Max Goodman, and I was lucky because he always used the same birth date, unlike so many of our immigrant forebears.
Even uncommon Jewish names can be held by more than one person or couple in NYC. I was searching for documents for the couple Lena and Sam Citron. I found the naturalization papers for Lena Citron, and her husband's name was Sam, and the papers had the correct year of birth for her. I thought I'd hit the jackpot - until I read the papers, and saw this couple was born in Galicia. The correct Lena and Sam Citron were from Bialystock. I could hardly believe it - there were two couples in New York City, both named Lena and Sam Citron, both who immigrated in the early 1900s.
So, as others have suggested, check to make sure you have the correct Hershkovitz family. Check ages of parents, the years the parents immigrated to US, the occupations of the parents, etc. These need to match up with information in other census records for the family.
And - it may be that the children were given up for adoption, or sent into foster care through what we now call Jewish Family Services, or taken in by relatives.
Lock/Lak/Lok and Kalon in Zagare/Joniskis, Lithuania
Olitsky in Alytus, Suwalki, Poland/Lithuania
Gutman/Goodman in Czestochowa, Poland
Lavine in Trenton, New Jersey and Lida/Minsk gub., Belarus