Kinderdijk is Children Dike, where the windmills are.
Long ago the letter IJ used to be the 25th letter of our Dutch alphabet, but it had to make place for the foreign Y which we call i-grec ( pronounced as ee-grec) and the IJ or ij had to be listed onder I or i. However we have so many names beginning with IJ or ij that we cannot ignore this letter and have to treat it as one letter.
Foreigners always ask me why are these letters written with two capital letters at the beginning of a name. I say then:"because they cannot be separated, they represent one sound. IJmuiden, IJssel, IJlst...We use this letter ij frequently and in scrabble we are not allowed to use aY or y instead. . So I hope everybody understands that we have more words starting with IJ than with Y in Dutch.It's pronounced like "ei"in leisure not like "e"in let. In Dutch dialects it's pronounced as "ee" like in we. Did I answer your question? ;)
In winter we skate on "ijs"( ice) on the river IJssel. The English word idle is almost the same in Dutch but spelled like "ijdel". More words with a similar meaning:
The Y however is substituted by "J" in Dutch at the beginning of a word, but has the same pronunciation as "y"in yes, you, year, yoghurt, yen, etc..
In our dictionaries we have only 14 words starting with Y. So it's not fair not to mention the IJ or ij.