I have been researching Kantners in Berks & Schuylkill, and when I sent my previous reply, I showed a Frank Kantner, son of John, but I now know that that one died in 1864, so he isn't the one you're looking for.But the following from the census may help:
1840 (Womelsdorf) Margaret Kantner, age 40-49; 1 male age 5-9; females: 1 age 15-19, 1 age 10-14
1850 (Womelsdorf) Margaret Contner, 60, & Frank, 18, living with Jno. Kintzer, 38, & Lucy A., 30 [Lucy may be Frank's sister?]
Israel Contner, 24, tailor, living with Henry Seagrist, 15, & Reuben Schwalm, 22 [probably just roommates]
1860 (Womelsdorf) Israel Kantner, 32, tailor Margaret, 72 Franklin, 25 Sarah Kalbach, 65 David Kalbach, 26
1870 (Womelsdorf) Frank Kantner, 34, cigar manftg. Emma, 26 William, 8; Kate, 6; Matilda, 4; Anna, 2; George A.,1
There is certainly a good possibility that Frank is Margaret's son, and that her husband died before 1840.Since there are many missing census records in Berks for 1830 and 1840, it's kind of hard to draw inferences by looking at who disappears from the census, but two possibilities might be Adam Kantner and Valentine Kantner, each of whom appears in Heidelberg Twp. in 1830 but not in any later censuses (at least in Berks).
Hope this helps.I'm trying to get around my brick wall (the parents of Sarah Elizabeth Kantner b.1832), and I've picked up a lot of extra info in the process.