Chosen Solution

My kid went through the “slip n slide” with the phone in his pocket, and now the phone wont turn on.

Take it to a repair store that offers a water treatment service, I recommend sooner rather than later as if left too long then there could be no hope to get it working again. Or alternatively if you want to give it a go all you need is the screw drivers a tooth brush and some isopropyl alcohol, pull the motherboard out of the phone and get busy with the tooth brush and alcohol, I also like the bath the mother board in the alcohol, if the corrosion is really bad a reflow machine may be required to remove the metal shields to clean under. Good luck