a theory on children's stages of play
... that American sociologist Mildred Parten developed a theory on children's stages of play?
... that American sociologist <a class="mw-redirect" href="./Mildred_Parten" id="mwAec" rel="mw:WikiLink" title="Mildred Parten">Mildred Parten</a> developed <b id="mwAeg"><a href="./Parten's_stages_of_play" id="mwAek" rel="mw:WikiLink" title="Parten's stages of play">a theory on children's stages of play</a></b>?