spar varnish is the best for this purpose but shellac will answer.
The one suggested in the drawing has red wheels with the remaining parts of the kiddie kar finished natural with spar varnish.
Outside of mahogany planking, finished in natural wood with spar varnish.
It will be necessary to protect it from the weather when not in use and frequently give it a coat of paint or spar varnish.
For the back yard, cut a paint barrel in two or coat a tub inside with spar varnish.
After the last coat of shellac is dry apply one coat of spar varnish.