The arrangement started last year after Colletti met Charlie Interrante, 25, at a magazine photo shoot for new mothers. Interrante mentioned her trouble nursing her son, Mateo, now 18 months old. She wasn’t able to pump her own milk for Mateo at her job as a barber, and Mateo had trouble digesting formula, Colletti said. Colletti offered to feed him along with her own son Lucian, now 16 months — and the women became “inseparable,” Colletti said. The babies, too.