I find sunscreen incredibly hard to get out of the kids white clothes (the few they have). Could it be suncreen? I can't get it out with pretreaters - i might need a rust remover too.

Steps for removing sunscreen stains
•If iron content in water is not an issue: pretreat the stain with a heavy duty liquid detergent or make a paste with powder detergent/water and let this set on fabric at least 30 minutes or overnight.Then launder as usual. Check clothing before drying. If stain remains, repeat.
•If the water has a high iron content, use a water softener . Be sure to wash and rinse clothing in warm water treated with a water softener.
•High heat and chlorine bleach can make the problem worse if there is iron in the water.
•If stain is still present, launder with a commercial rust remover. Commercial rust removers are for use only on white or colorfast fabrics.