The nature of a marker pen is such that the stains are really tough to remove. Here is a hack to tackle bad marker stains with items easily available at home in 3 steps.
Prepare a mixture of one tablespoon each of milk, vinegar, borax and lime juice in a bowl.
Using a dry cloth, apply the mixture directly to the stain and let it sit for 15 minutes.
Take a dampened sponge and use it to dab at the fabric until the stain comes away.
In case the above process doesn’t do the trick, dilute 2 cups of bleach in water and dip the stained part of the clothing in it. For any kind of stains, it is best to soak the stained area in warm water before beginning the cleaning process. The ink may be permanent but the stains need not be.