When do you start or let your child use baby powder?

Hey, I would suggest do not use powder at all, since powder when sprayed its particles may get inhaled by the kids and it may cause asthma or can cause irritation. Please read this article and you can find in detail that powder is not advisable to be used. https://www.theguardian.com/lifeandstyle/2013/jun/23/should-i-stop-using-talcum-powder