How would I go about inserting a UIViewController inside a UICollectionView Cell?
What Daniel said is correct, however if you have to add many childViewControllers to a UICollectionViewCell or UITableViewCell, it could be cumbersome to maintain.
Here's a nice post from Suroush Khanlou which handles that complexity and simplifies the process.
http://khanlou.com/2015/04/view-controllers-in-cells/