A young mother and her baby walk along a street .
a young mother and her baby are walking down a street
A young mother and her baby walk along a street.
a young mother and her baby are walking down a street
Walking down a street and walk along a street mean the same thing, that a walk is being done on or near a street.
Walking down a street and walk along a street mean the same thing , that a walk is being done on or near a street .