As a Kendoka (and Iaidoka) myself, it's great to see a Playmobil representation.
The white top works (indigo blue is more common - white means purity and is generally worn by women (women would generally train in naginata, not sword, today women training in kendo is more common).
We do not wear "belts" on the outside of the uniform. The obi (belt) is worn under the hakama (split skirt) and can not be seen. It is between the second and third layer of the obi that the saya (scabbard) is placed.
As for the red hakama, Kendoka would not wear that. Temple maidens are the only individuals I know of that wear red hakama. They also happen to wear white keikogi (tops).
The short staff he holds would be perfect as a Jo. Jodo is a valid samurai art as well. In fact, Jodo, Kendo and Iaido all are under the governing body of the Zen Nippon Kendo Renmai (ZNKR) which translates to "All Japan Kendo Association".