WordNet
n. toilet consisting of a small seat used by young children [syn: potty seat]
Wikipedia
A potty chair is a proportionately small chair or enclosure with an opening for seating very young children to "go potty." It is a variant of the close stool which was used by adults before the widespread adoption of water flushed toilets. There are a variety of designs, some placed directly over the toilet called "Toilet Training Seats" so the egested fecal material drops directly into the toilet bowl thereby eliminating manual removal and disposal of the said waste from a receptacle beneath the hole which is often a bag or receptacle similar to a chamber pot, if the child stays in the correct position, of course. Potty chairs are used during potty training, a.k.a. toilet training.
Usage examples of "potty chair".
The customer capitulated, wrote a check, and left the shop in high glee, carrying a potty chair with sawed-off legs.
Either sex could use the solid-collector funnel, as that was set in a sort of potty chair with handholds to keep the floating body proximate.