Does anyone know how much AAdvantage miles are needed to redeem flights for an infant?

Planning a Perth - New York City & Vancouver trip end of this year with a probable baby (2-3 months old at time of travel).

Does anyone know AA costs requirements for award redemption with infant.

Website says “portion of adult fare” but nothing to be found when redeeming miles???

Depends on the airlines. Generally, unless you are redeeming a seat for the infant, no extra miles will be needed. But some airlines may require you to pay a portion (usually ~10%) of the airfare for shared seats. You need to check with the operating airline as AA do not charge those fees.