Hi a warm welcome to the forum. You need to start by looking at, or identifying the theories of development, then researching them and then you'll be in a position to explain them xx
Your
framework will depend on your
home nation, eg. if you work in the early years sector in England the framework will be the EYFS.
A
level 3 handbook - page 68 of the amazon preview, will support this research as will any materials your tutor provides xx
Best wishes