The recursion is to not overload the thread so you need to create two functions something like this:

function buildChildren(childrenObject){
    let length = childrenObject.length; // Brought outside the loop due to improved execution times.
    for (let i = 0; i < length; i++) {
        let child = childrenObject[i];
                // Do stuff with the child here, such as building it and attaching it do the DOM.
        fetchChildren(child);
    }
}

function fetchChildren(child){
    if (child.children.length > 0) {
        buildChildren(child.children);
    }
}

This is essentially what you want to do. This does not throw recursion errors but will take a while if the array you have is of significant size.