How can I remove stains from my mattress and carpets

http://www.housecleaningcentral.com/en/cleaning-tips/stain-removal/clean-mattress-stain.html

https://www.thisoldhouse.com/how-to/how-to-remove-every-type-carpet-stain

You can try a solution of OxiClean and water for the stains, but it must be mixed just prior to use, not stored to be effective. You might invest in a waterproof mattress pad to protect your mattress. The best solution might be to not let your grandson's drink beverages other than water in your bed. If they are drinking milk or juice before going to sleep it can lead to tooth decay. A carpet cleaner that I've found effective is Spot Shot.

Mix hydrogen peroxide and distilled water on a spray bottle, peroxide in first, 1:1 ratio. Spray any natural body fluid(milk counts) with it, let it fizz and bubble, then pour on regular old backing soda. Let dry...brush well, vacuum off.

For mattress stains, this guide has every type covered: https://www.hometalk.com/posts/clean/mattress/how-to-clean-a-mattress-44430230