How to create a child object of an object with a specific tag?

I would like the spheres that appear after pressing PLAY to be children objects of the object with the PLAYER tag.

How to do it?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class PathPlacer : MonoBehaviour {
 
    public float spacing = .1f;
    public float resolution = 1;
 
 
 
    void Start () {
        Vector2[] points = FindObjectOfType<PathCreator>().path.CalculateEvenlySpacedPoints(spacing, resolution);
 
 
        foreach (Vector2 p in points)
        {
            GameObject g = GameObject.CreatePrimitive(PrimitiveType.Sphere);
            g.transform.position = p;
            g.transform.localScale = Vector3.one * spacing * .5f;
        }
 
        }
 
    }

You can assign the parent object of the newly created GameObject:

g.transform.parent = someObject.transform;

You can get object by tag using GameObject.FindWithTag.