There are a couple of issues surrounding the use of talcum powder on babies. Firstly, there have been reports of breathing problems caused by babies inhaling talcum powder. Also, there have been some studies that have indicated a connection with the use of talcum powder by women and ovarian cancer. It is thought that small particles of talcum powder travel up the fallopian tubes to the ovaries, even in young babies, and can precipitate ovarian cancer.
I personally have never recommended the use of talcum powder with any baby, especially if it is used in large quantities and is shaken over the baby, as the baby can inhale the powder dust, which can bring about an asthma attack in allergic children.
At a practical level, it tends to clog the pores and I do not feel that it is particularly good for skin care. If you want to use talcum powder on your baby, I would recommend that you use cotton wool to dab it on gently, so that the powder is not wafting over the baby, and that it is best not used at all in the nappy area of little girls.