A baby boy is sitting in the baby swing at a park .
There is a baby at the park .
A baby boy is sitting in the baby swing at a park.
There is a baby at the park.
The first sentence establishes there is a baby boy at a park, the second has a baby as well and has the same setting, the park, just with less details.
The first sentence establishes there is a baby boy at a park , the second has a baby as well and has the same setting , the park , just with less details .