This study shows that chickens are smarter than most people give them credit for, which is true. But it does not say or show that chickens are smarter than human toddlers. In fact, it seems quite cautious to avoid making such bold statements. The most direct comparison that it makes is in delayed gratification (self control) where the chicken held out longer for a bigger reward than the toddler did. And that's about it. That's a very far cry from the sweepingly broad statement that a chicken is "smarter than a toddler"...Okay then here you go an in depth study on chickens and their cognitive abilities and psychology
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5306232/