Grandma watched her grandson with a beaming smile.
Tips
grammar
ABB-pattern adjective (笑 + 吟吟). These reduplicated descriptives are usually used adverbially with 地, e.g. 笑吟吟地说 (said with a smile). Compare 笑嘻嘻 (grinning) and 笑哈哈 (laughing heartily) - same pattern, different shade of smile.
