Kids Bicycle Saddle Little Rider Child Seat Bike seat Kids for Boys 14” to 24” Bicycles Kids Seat

My son is 4yrs old, using training wheels can a bike with training wheels use this seat?

Is the seat covered with leather or plastic?

What are the dimensions of the seat?

What diameter seat post will it fit? My son has a 1” diameter (25.4mm) seat post. Just want to make sure before I purchase, thanks.