Adults, and children and infants all have varying butt sizes. It’s a matter of fact. Even thin people and fat people have varying sizes. All toilets to date only have seat covers of a single size. Occasionally, there will be more thoughtful toilet owners who will have children seat covers which are a fit over the original toilet seat cover.
What I propose is a multi seat cover all fitted as one piece onto the toilet bowl. The top most layer is the one with the smallest circumference and as you lift up the varying toilet seat covers, the circumference of the seat gets larger and larger to accommodate varying sizes of people. I am not able to illustrate it with a picture, but the concept is similar to the toy which is a single doll and you open it up and a smaller doll is within and this goes on till the last final doll which is the smallest.
Probably not the most revolutionary idea, but it could be much less of a hassle for million of parents who bring their kids out and have no means for their kids or infants to utilize the public toilets effectively. They usually just carry their kids while the kid does their ‘business’ dangling from their parents hands. (Neat!)