The Lostprophets frontman will appear at a Cardiff court on Wednesday (December 19).
The singer is charged with conspiracy to engage in sexual activity with a female aged under 13 and possession and distribution of indecent images of children.
Two women aged 20 and 24 from Doncaster and Bedford are also facing similar charges, and have been questioned at Cardiff Bay police station.
Senior investigating officer Peter Doyle said: "Specially-trained staff are available to speak to anyone with concerns or information regarding this investigation and a dedicated telephone number has been set up.
"I want to encourage anyone who has any concerns or information which they think may be relevant to contact us.
"Safeguarding children involved in such cases is always a high priority and as such measures have already been taken."
Watkins co-founded Welsh band Lostprophets in 1997, and the group have sold around 3.5 million albums worldwide.
Their 2005 album Liberation Transmission reached number one in the UK, while their fifth LP Weapons hit number nine earlier this year.