They're both correct; just slightly different examples of coordination.

1. I told him to go to the mall and to the park.

2. I told him to go to the mall and the park.

In 1, the coordination is between the two underlined PPs (preposition phrases). In 2. it's between the two underlined NPs (noun phrases).

Both sentences are perfectly grammatical and have the same meaning, so it's a free choice between the two, though 2. is slightly more efficient.

PaulM

thank you for teaching me