I want to build 6' long 15" deep 4'high shelf. Needs to be extremely sturdy. What wood should I use?

This will be a toy shelf for my nursery school clroom. I do not wish to use MDF due to the formaldehyde. What wood? Where to purchase material? can anyone recommend a particular building plan? Needs to be sturdy enough to handle being beat up by kids all day long for 30 years.I'm really not interested in Ikea grade furniture. My grandmother opened this school in the 70's and the furniture would still be good if it weren't out dated. I tried to find more modern looking pieces but anything pre-made is all crap. I can build it if someone will direct me!