ソースコード

using System.Linq;
using UnityEngine;

public sealed class Example : MonoBehaviour
{
    private void Update()
    {
        var spriteRenderers = GetComponentsInChildren<SpriteRenderer>();

        var left   = spriteRenderers.Min( x => x.bounds.min.x );
        var bottom = spriteRenderers.Min( x => x.bounds.min.y );
        var right  = spriteRenderers.Max( x => x.bounds.max.x );
        var top    = spriteRenderers.Max( x => x.bounds.max.y );
    }
}