The ornamental design for an inflatablechildseat, as shown and described.
FIG. 1 is a front view of an inflatable child seat of the present invention;
FIG. 2 is a rear view of the inflatable child seat of FIG. 1;
FIG. 3 is a top view of the inflatable child seat of FIG. 1;
FIG. 4 is a bottom view of the inflatable child seat of FIG. 1;
FIG. 5 is a perspective view of the inflatable child seat of FIG. 1;
FIG. 6 is a front perspective view of the inflatable child seat of FIG. 1 shown in use with a chair, wherein the chair is shown in broken lines and forms no part of the claimed design; and,
FIG. 7 is rear perspective view of the inflatable child seat of FIG. 1 shown in use with a chair, wherein the chair is shown in broken lines and forms no part of the claimed design.