Abstract: A modularly constructed child's chair includes a chair module which is equipped with a back rest, a side rest, and a seat. The chair module is equipped with a seat hole and with a chair fastening device for fastening the chair module on either the upper part of a base unit or the upper part of a toilet. A removable seat hole cover, which covers the seat hole, includes a cover fastening device for fastening the cover on either the chair module, or on a base unit. A base unit which fits the chair module includes receivers for the cover fastening device and for the chair fastening device. In addition to other accessory modules, a support module, serving as a front and crotch support, along with a potty module, are part of the modularly constructed child's chair.