I love Japanese tongue twisters. They're so much fun.
My favorite ones are:
庭には二羽鶏がいる。
(niwa ni wa niwa niwatori ga iru)
There are two hens in the garden.
この布は名の無い布なの。
(kono nuno wa nano nai nuno na no)
This cloth is one that has no name.
隣の客はよく柿食う客だ
(tonari no kyaku wa yoku kaki kuu kyaku da.)
The customer next to me is one that eats kaki fruit often.
There are extended versions of the ones above, too, so you can try to challenge yourself! *g*
There are very cute ones that are more for really young kids such as:
ママのマカロニマママカロニ、パパのパパイヤパパパイ ヤ
(mama no macaroni = mamamacaroni; papa no papaya = papapaya)
There's so much more! What's your favorite one?
If you want to find more just google for "早口言葉" (hayakuchi kotoba). (^__^)b