How can I clean my old wagon without ruining the lettering and paint

Try Williams Car cleaner (No water required. Available from Ideal World - TV - UK May be in your country too

Scrub brush, warm water, detergent or soap, and a hose to rinse it off. What have you been doing that removes paint?

If it's made of wood, I would start with Murphy's Oil Soap and a rag.

dawn detergent and warm water just don't scrub too hard use a soft sponge

gently, nothing abrasive or caustic; no 'green scrubbys' or stiff brushes. even diluted DAWN can be used carefully and well rinsed with clear water; DRY DRY DRY -- use a hair drier if necessary to get it as dry as possible as quickly as possible; then a good paste car wax if a metal wagon, or a good wax for wood -- such as HOWARD'S Feed N' Wax.

Thanks. Haven’t tried anything yet. I was concerned because I know that sometimes paint has oxidized and seems to rub off. I will try y’all’s suggestions and let you know how it goes