The four stages of play are solitary, parallel, onlooker, associative, and cooperative. Solitary play refers to when a child plays alone, without interacting with others. Parallel play is when children play alongside each other, but do not actively engage or interact with one another. Onlooker play is when a child observes others playing but does not join in. Associative play involves children playing together, sharing materials, and loosely interacting with each other. Cooperative play is the highest level of play, where children work together towards a common goal, take on roles, and actively engage with one another.