What are the main theorists and theories in child language acquisition?

The four main theorists and theories in the field of child language acquisition are as follows:

The innateness theory - Noam Chomsky.
This theory suggests that children have an innate ability to learn language, which allows any child who are in the critical period to be able to learn a language. Chomsky argues that children have something that he has coined as the LAD (Language Acquisition Device) which is a thing in a child's brain that allows them to be able to pick up any language, regardlesss and argues that children simply do not imitate language that they hear around them. Chomsky has one of the most forward theories in terms of language acquisition, and many other theorists support this theory in some ways. However, one argument that does not support the Innateness theory is the simple argument of accents. Children must imitate at least part of their surroundings because this is how different regional accents are developed and how different languages are developed.

One of the biggest opposing arguments to Chomsky's Innateness theory is The Imitation theory - B.F Skinner.
The imitation theory states that children only learn language through listening and copying the language that they hear around them. As soon as children have mastered their mouth muscles and voice boxes, this is when children begin copying what is being said, mainly by their primary caregivers. 
This theory, whilst on the surface may seem fairly obvious, is flawed in many ways, with one of its only supporting arguments being the acquisitions of accents, which was noted above. But if children only learnt the language around them, they wouldn't know the rules of grammar and so would continue to make mistaked throughout their lives.

The Input/Interaction Theory - Jerome Bruner
This theory relies on the idea that children require a lot of interaction with people, mainly their primary caregivers, to really grasp the language they are learning. This theory favours Chomsky's Innateness Theory, and Bruner coined another term which partners with Chomsky's LAD. Bruner came up with the idea of the LASS (Language Acquisition Support System), which argues that children do have an innate ability to learn and acquire language, but also require the interaction of other users of the same language to excel in their learning.