MADRID—At least 29 Africans, including seven children, died last week while trying to reach Spain’s Canary Islands on a smuggling boat, according to information released Monday from a U.N. migration agency and a Spanish migrant charity in touch with victims’ relatives. Spanish maritime services on Friday rescued 27 migrants and recovered 4 bodies in the boat that was spotted by a fishing vessel 500 kilometers (300 miles) south of El Hierro, an island in the Canary archipelago off northwest Africa. But at least 24 more people were on the boat when it left Aug. 15 from Dakhla, a port city in the disputed Western Sahara, said Helena Maleno, founder of the Walking Borders non-profit group. Maleno’s organization came up with the figure after conducting extensive interviews with relatives looking for their loved ones. She said only one of the eight children traveling on the boat survived but the girl lost …