South Wales Police said Angharad Williamson, 30, from Sarn, will appear at Cardiff Magistrates’ Court on Friday.
She becomes the third person charged with the five-year-old’s murder.
The victim’s stepfather John Cole, 39, and a 14-year-old boy, who has not been named because of his age, have also been charged with murder.
It comes after the little boy was found dead in Ogmore River near Pandy Park in Bridgend on Saturday July 31.
Police made the discovery when they responded to a report of a missing child at 5.45am.
Princess of Wales Hospital staff confirmed the child was dead.
Flowers, toys and teddies were left in front of the police cordon by the river where the boy’s body was found.
There have been many tributes for the little boy who family friends described as “kind, funny, polite, handsome and clever”.