The playing children seemed happy and energetic. Here 'playing' is a/an -

• The playing children seemed happy and energetic. Here 'playing' is a - Participle.

Participle:
- It is the form of a verb that usually ends in "ed" or "ing" and is used as an adjective:
- Participle একই সাথে Verb ও Adjective এর কাজ করে। 

Participle মূলত: তিন প্রকার: 
1. Present Participle. Ex: Do not disturb a sleeping dog. 
2. Past Participle. Ex: This is a book written by Charles Dickens. 
3. Perfect Participle. Ex: Having eaten rice, he went to bed.

• The playing children seemed happy and energetic - এই বাক্যে playing, noun word children কে modify করছে।
- তাই এটি adjective এর কাজ করছে।
- verb+ing যখন adjective এর কাজ করে তখন তাকে participle বলা হয়।