After getting their presents, the children were all smiles.
Tips
history
Attested in Qing novel 《镜花缘》第九十九回: 穿过牌楼，人来人往，莫不喜笑颜开 — describing a festive, sunlit market where every face has brightened up. The sense of a face 'opening' (颜开) into a smile has stayed fixed.
memory
Read the four characters as a sequence: 喜 (joy) → 笑 (smile) → 颜 (face) → 开 (opens). Joy smiles, face opens — a little slow-motion GIF of a grin.
