Hannah Rothstein, 7 months old, has double thighs and a dimpled bottom, but very svelte German underwear. She can still fit into her birth-to-3-month-old clothes because she lacks her peers' familiar bulge in the rear. She can sleep all night without a diaper. And during the day, every so often, after her mother, Melinda, of Newton, Mass., places her on a plastic potty and makes a little "pss-wss-wss" sound like the one used to call a cat, Hannah uses the toilet.

For many parents in the United States, the idea of potty training before a baby is able to walk, or even before age 2, is not just horrifying but reprehensible -- a sure nightmare for parents and baby, not to mention a direct route from the crib to the psychiatrist's couch. But a growing number of parents are experimenting with infant potty training, seeing it as more sanitary, ecologically correct and likely to strengthen bonds between parent and child.

About 2,000 people across the country have joined Internet groups and e-mail lists to learn more about the techniques of encouraging a baby -- too young to walk or talk -- to go in a toilet, a sink or a pot. Through a nonprofit group, Diaper Free Baby (www.diaperfreebaby.org), 77 local groups have formed in 35 states to encourage the practice. One author's how-to books on the subject have sold about 50,000 copies.

"It's just so simple," said Lamelle Ryman, who recently attended a support meeting at an apartment on the Upper West Side. Ms. Ryman, the mother of 7-month-old Neshama, added, "I feel like it's been such a gift in our relationship."