At least 2 days in advance: Make color flow bluebirds on waxed paper using pattern and tip 2. When dry, add tip 2 dot eyes with full-strength color flow; let dry. Attach lollipop sticks to backs of bluebirds with full-strength color flow; let dry.
Also in advance: Using flower nail and royal icing on 2 in. waxed paper squares, make 15 tip 102 wild roses with tip 2 dot centers and 6 tip 103 wild roses with tip 3 dot centers. Set all flowers on small flower formers to dry. For flower stem, use thinned royal icing to paint a 1 1/2 in. piece of uncooked spaghetti; let dry on waxed paper. When flowers and stem are dry, attach stem to a tip 102 wild rose and to beak of bird; let dry.
Ice cake sides, bottom of buggy and background areas smooth in buttercream. Pipe tip 44 lattice on bottom of buggy. Outline hood with tip 4 and fill in with tip 13 stars. Pipe tip 2A handle and top buggy rim (smooth rim area with finger dipped in cornstarch). Pipe tip 12 wheel rims with tip 6 spokes; add tip 6 dot hubcap. Attach flowers to bottom border with buttercream; add tip 352 leaves. Attach flowers to edge of hood; insert bluebirds.