Here is the "Four Questions" song I made up some years ago for my then-two-year-old. The tune is "For He's A Jolly Good Fellow," first part of the tune only. Any kid who can already talk can learn to complete each line. (Except 'vegetables' - a mental block for my son!)
First the Yiddish, the way we sing it:
א גאנץ יאר עסט מען חמץ
פסח עסט מען מצה
vegetables א גאנץ יאר עסט מען
פסח עסט מען מרור
א גאנץ יאר טינקט מען נישט איין
(waggle finger or shake head)
פסח טינקט מען צוויי מאל
(hold up two fingers)
א גאנץ יאר זיצט מען גלייך
(soldier-straight)
פסח זיצט מען אנגעליינט
(tip over dangerously toward one side)
And the English, which I just made up now, but it seems to work fine with the tune:
All year round we eat Chametz --
Pesach, only Matzah.
All year round we eat vegetables --
Pesach night, it's Maror.
All year round, we never dip --
(waggle finger or shake head)
Pesach we dip TWO times.
(hold up two fingers)
All year round, we sit up straight --
(soldier-straight)
Pesach we recline.
(tip over dangerously toward one side)
That's it! I find even the bigger kids like this easy song better than the longer chant they memorize in school.
Once your child knows the song, you can add the traditional sing-song introduction, "Mah nishtanah, why is Pesach night so different?" "?מה נשתנה, פארוואס איז די נאכט פון פסח אנדעריש פון א גאנץ יאר" or your preferred wording.