What should I be testing for to investigate soil safety for my school ?

Recently my school has decided to initiate a program in which it grows vegetables and keeping chickens for their eggs. I and a few of my friends have been tasked with heading the project and the first thing I need to do is test the soil for if it's safe enough for primary school kids working with the project and for animals. I just need to know what exactly to test for, I have already thought of testing for pesticides and fertilisers and maybe it's pH but other than that I have no clue.