This is part of an anti-LGBT hoax. Conservatives made up the lie that children were using litterboxes. They are equivocating "identifying with a gender that you weren't assigned at birth" with "identifying as an animal". It's like how conservatives said that if same sex marriage became legal, then people would start marrying their dogs.
Some people also speculated that the hoax began because some classes have litter buckets as part of school shooting preparedness.