The ornamental design for a triple babystroller, as is shown and described herein.
FIG. 1 is a perspective view of a triple baby stroller showing my new design;
FIG. 2 is a left side view thereof; the right side being a mirror image thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a back view thereof; and,
FIG. 6 is a bottom view thereof.
The broken line showing of the wheels and front step in the figure drawings is included for the purpose of illustrating environment and forms no part of the claimed design.