The word is playground.
playground
Yes it is. Play and ground is a word and it has a meaning
Play playpen playtime playground playmate
under-ground
backgroundbattlegroundcampgroundfairgroundforegroundplaygroundunderground
Underground.
Play playpen playtime playground playmate
"Underground" is a compound word with secondary stress on the second syllable ("ground").
Playtime
A sentence with a compound word is, He was excited about signing up to play football.
Yes, indoors is an adverb.Example: The children played indoors.Adverbs often answer the questions where? when? how? Where did the children play? Indoors.
A word for something that children play with is toy.