The 63rd Street and Central Park West entrance to the park is a direct line to the Heckscher picnic area.
Enter the park, walk down the path and cross the street.
At the bottom of the hill is Ballfield #4. Continue on the footpath on the right side (south side) of the Ballfields.
The next field is Ballfield #2 (less than 50 yards from #4). The Ballfield is on your left.
On your right, between the ballfields and Umpire Rock (aka Rat Rock) is the Heckscher picnic area.
Across the ballfields from the picnic area is Heckscher Cafe. You can get snacks and beverages here.