While I am very uncomfortable with feeding soy to infants  because of the possibility of hormone disruptions, preliminary studies are suggesting that food based sources of soy during early childhood and adolescence may protect against breast cancer.

"By comparing the highest and lowest soy intake values for soy-based foods such as tofu, miso and natto, Korde and co-workers at the National Cancer Institute calculated that women with the highest soy intake during childhood (ages 5 to 11) had a 58 per cent lower risk of breast cancer as adults as the women with the lowest soy intake as children.

The corresponding reductions for adolescent and adult intake were about 25 per cent, they said.

The underlying mechanism is not known, said the researchers, but they hypothesized that the oestrogenic effects of soy isoflavones cause changes in breast tissue during childhood that may decrease sensitivity to carcinogens later in life. A similar protective effect has been found in studies of overweight girls, perhaps because fat tissue also secretes oestrogens, said Korde."

Soy during childhood linked to lower risk of breast cancer

The Vitamin lady writes about protecting against breast cancer