I am an Anzu and I eat a balanced diet of plants, insects and ….. children!
Anzu was an oviraptorosaur and would have been a danger to young T rex before they had even left the egg. This dinosaur is hypothesized to be an omnivore and I can definitely see it eating a T rex egg or scooping up an unsuspecting hatchling.
Besides Anzu young T rex would also fear predators like Archeroraptor, Pectodon and possibly Struthiomimus.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3960162/