Is it possible to add an Object inside a Child (Obj) in firebase?

I am currently starting to use firebase and I want to implement a database in my Android app, I am trying to upload two Objects, for now I have uploaded a Person type Object in the following way:

in OnCreate :

    mFirebaseDatabase = FirebaseDatabase.getInstance();
    mDataBaseReference = . 
 mFirebaseDatabase.getReference().child("Personas");

Then to add my object to the database:

mClientesDataBaseReference.push().setValue(nuevaPersona);

Achieving upload this:

personas : {
 "dsgasdgjbnakjds" : {
      "Nombre" : "Lalo",
      "FotoId" : "1",
      "edad" : "18",

      } 
 }

My object is something like this:

     public Cliente(){
         //Variables de tipo String
         nombre = "";
         FotoId = "";
         Edad = "";
         // Variable tipo Mascota
         mastoca = new Mascota();
    }

    public Mascota{
      //String
      Nombre = "";
      Edad= "";
    }

However, even declaring the pet as part of the Persona object, it does not appear in the database.

I would like to be able to add the Object ( mascota ) within this same Object of persona and achieve something similar to this:

personas : {
 "lksdjnflkasdg" : {
      "Nombre" : "Lalo",
      "FotoId" : "1",
      "edad" : "18",
      "Mascota" : {
           "nombreMascota" : "LittleDog",
           "edadMascota" : 3
      } 
 }, 
 "lkjndslfknlksdn" : {
      "Nombre" : "Roberto",
      "FotoId" : "2",
      "edad" : "20",
      "Mascota" : {
           "nombreMascota" : "LittleDog",
           "edadMascota" : 5
      } 
}

Thanks