The JSON of Tags as well as its child Tags are the desired result. Below is the JSON response for a single Tag(without child) I'm getting from https://{$HOSTNAME}/content/cq:tags/{$TAG_PATH}.json
{"jcr:primaryType":"cq:Tag","jcr:mixinTypes":["rep:AccessControllable"],"jcr:createdBy":"admin","jcr:t...