There is no need to throw away children's jeans and pants that has grass stains on the knees and bottom because there is a way to get those stains out and keep the clothing looking like new.
One way is to scrub the stained area with Fels Napatha soap before you put it into the washing machine. This soap is available in the laundry section of the supermarket, rather than in the toiletry section. Keeping a bar of soap on hand will help you cut down on clothing costs and eliminate the need for making sure the children have old clothes on when they go out to play.
For residents of the United Kingdom, there is a product known as Dylon that makes an excellent grass stain remover. This product comes in small bottles and there are different types for different kinds of stains. The stains you can remove with the various types are listed on the side of the bottle and one of them is the green coloring of grass. If you can catch the stain as soon as it appears on jeans and pants, it is easier to remove than when it has had time to dry into the fabric. In this case, a simple scrubbing with dishwashing liquid will do the trick. Then, you can just launder the jeans and pants in the normal fashion.
Vinegar has many household uses and is not just a condiment for adding flavour to food. In order to take out grass stains from clothing, you can soak the stained area or the full garment in vinegar for about an hour. Scrubbing the area every now and then will help to loosen the stain that comes from the chlorophyll in the grass. When you wash it with your regular laundry detergent, this will remove any scent of vinegar.
Another age-old home remedy for the removal of grass stains from clothing is baking soda. Make a paste of baking soda and water, with a little vinegar added to the mixture. Use a scrubbing brush on the stained area and this will really help your cause, because vinegar contains a compound that actually lifts the grass stain from jeans.
How about white toothpaste for removing grass stains? This little-known trick works well, especially on denim material. You do have to be careful though because only the non-gel form of toothpaste works in this manner. Cover the stain with toothpaste and scrub it vigorously. Then wash the jeans in the washing machine.
All of the above suggestions are worth keeping in mind to get rid of those grass stains which spoil the look of those jeans or pants.