Laundry Stain soak

My toddler is a dirty little boy and his clothes are constantly covered in mud, grass, etc when he comes in the house. Usually I just soak his clothes in a bucket of water for a day before washing them, and sometimes I’ll add some laundry soap to the bucket. Is there a better method for getting the stains out? Some of his clothes have permanent mud stains and I wonder if there’s a better stain remover that I can add to my bucket of water rather than just regular laundry detergent.