"Treat sizes" refers to the different portions or amounts of treats that are available. It means that there are various sizes or quantities in which treats are sold or given. Full definition
I feed a little of whatever we are eating, chicken, turkey, salmon, beef or pork, or liver in very small treat size quantities. (miniatureschnauzer.ca)
I just cut up the lamb one yesterday into nice small training treat sizes - and no crumbling. (leerburg.com)
These bulbs help growers maintain better treating the size with their plants and boost photosynthesis. (doublechindiary.com)