If the items are for babies up to 86 cm, classify the set under HSN 6111 (knitted) or HSN 6209 (non-knitted/woven). For older children, classify the top and pant separately under their respective Chapter 61 (knitted) and Chapter 62 (woven) headings based on their fabric composition. The GST rate is generally 5% for items under ₹1,000 and 12% for those above.