The science that goes into building a toy wagon?

for my design class i need to present to my classmates the chemistry, biology, and physics that goes into designing a toy wagon for children.



if you can think of any suggestions (especially for biology) i'd REALLY appreciate it. :) thank you!The science that goes into building a toy wagon?
For biology, I guess you would want to use materials that aren't toxic. For example, if you paint the wagon red, you wouldn't want to use lead-based paint because kids will sometimes lick paint or eat it if it's peeling off the wagon.



You might coat the wooden parts in a shellac or something, so the kids wouldn't get splinters from the wood.



Both of those are health issues, which is part of biology (also chemistry for the paint and shellac). I guess the wood needs to be a certain age so it's thick and strong enough - that would be botany.



Physics would be that you'd calculate the force needed to pull it and get the size and placement of the wheels and length of the handle from that.