[{_id:"Toy",name:"Toyname",child:[{item:"Toy1",isActive:"1",Type:"New"},{item:"Toy2",isActive:"2",Type:"Old"},{item:"Toy3",isActive:"1",Type:"New"}]}]

db.collection.aggregate([{"$match":{"_id":"Toy"}},{"$addFields":{"child":{"$filter":{"input":"$child","as":"c","cond":{"$eq":["$$c.isActive","1"]}}}}}])