Many people believe that such activities as owning a pet, taking care

Many people believe that such activities as owning a pet, taking care of another's pet, and, of course, babysitting an infant not only confer the capacity of friendship on a child but also develop role-taking skills, since that child must put him- or herself in the pet or infant's situation and imagine how that pet or infant feels.

not only confer the capacity of friendship on a child but also develop --> uses the correct Idiom: "Not only..But also" --> hence is correct.

confer the capacity of friendship on a child but also are developing--> Should use the correct Idiom: "Not only..But also" --> hence is not correct.

are conferring the capacity of friendship on a child but also are developing--> Should use the correct Idiom: "Not only..But also" --> hence is not correct.

not only confer the capacity of friendship on a child, they are also developing--> Should use the correct Idiom: "Not only..But also" --> hence is not correct.

are conferring the capacity of friendship on a child, and they are also developing --> Should use the correct Idiom: "Not only..But also" --> hence is not correct.