Database
[{"name":"Man1","Childrens":[{"name":"Children 1","age":"12"},{"name":"Children 2","age":"18"},]},{"name":"Man1","Childrens":[{"name":"Children 1","age":"44"},{"name":"Children 2","age":"55"},]},{"name":"Man1","Childrens":[{"name":"Children 1","age":"22"},{"name":"Children 2","age":"33"},]}]
Query
db.collection.find({Childrens:{$elemMatch:{age:"18"}}},{Childrens:{$elemMatch:{age:"18"}},_id:0})