Kawaii means cute, so the term can describe many kinds of clothing. A pastel dress with bows may be kawaii without being Lolita. Sweet Lolita is more specific: the garment and coordinate follow a recognisable silhouette and use supporting pieces to complete it.

The overlap is real. Both can use soft colour, fruit, animals, hearts or other playful motifs. The difference becomes clearer when you look beyond the print.
Kawaii describes an aesthetic
A kawaii dress may be casual, fitted, oversized, short or designed without a petticoat. It can draw from streetwear, loungewear, party clothing or many other fashion directions.
Pastel colour is common but not compulsory. Black kawaii fashion can use the same playful motifs with a darker palette. The term does not prescribe one skirt shape, neckline or coordinate formula.
Sweet Lolita uses a structured silhouette
A Sweet Lolita dress usually has enough skirt width for an A-line or bell-shaped petticoat. The bodice, waist and hem are designed as part of that proportion. A JSK may need a blouse, while an OP resolves the upper body in the dress itself.
The full coordinate also matters. Legwear, shoes and headwear support the dress rather than operating as unrelated cute accessories.
Check construction instead of labels
Retail titles sometimes use several search terms at once. Do not rely on a product being called kawaii, Lolita or Japanese style. Check the actual shape and measurements.
Look for skirt width, waist placement, lining, closure and the way the bodice is finished. Confirm which pieces are included in the selected option. A photograph of a full coordinate may advertise only the dress.
Coordinate pastel colour without flattening it
Choose a main colour from the garment and repeat it once or twice. Cream or white can separate similar pastel shades when an exact match is unavailable.
Print scale should guide the accessories. A dense print can take plain socks and quieter headwear. A simple pastel dress can support a more decorative blouse or bag.
Choose the term that matches the garment
Use kawaii dress when the main point is a cute aesthetic across a broad range of silhouettes. Use Sweet Lolita dress when the garment is constructed and styled within Lolita fashion.
One term is not a higher-quality version of the other. They answer different questions. The useful distinction is whether you are choosing a cute dress on its own or building a complete Lolita coordinate around a specific silhouette.