The ornamental design for a babybathseat, as shown and described.
FIG. 1 is a perspective view of a baby bath seat showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of portions of the baby bath seat is included for the purpose of illustrating environmental structure and forms no part of the claimed design.