The former Friends star recently took a low-key trip to the Casa Hogar Sion orphanage in Tijuana.
Aniston and ex-husband Brad Pitt - who has three adopted children with partner Angelina Jolie - have both donated money to the institution, reports U.S. magazine Star.
Co-founder Carmen Gonzalez says Aniston "got on with all the children, but spent most of her time with the babies," adding, "She loved them. She was in the nursery for a long time playing with them."
The story follows weeks of tabloid reports suggesting Aniston is keen to start a family.