How to define a child node in Firebase by IONIC 3

Question

Hello, I am working on a project with Firebase Realtime Database and Ionic 3, but I have a problem with the child node.

for example: My son is "Lkucxf041hhfrkn3tiq", how to set this son to "test"?

My code is:

sendMessageModule(){
    this.db.database.ref('/tasks').child(this.uid).push({
      taskM: 'onM'
    }) 

I tried that way too, but I didn’t succeed:

sendMessageModule(){
    this.db.database.ref('/tasks').push({
      taskM: 'onM'
    }) 

Thank you all!