Children don't literally know what they like yet. When it comes to different types of music, and other things for that matter, there are no preconceptions about it when it comes to children. They won't turn away from new things, even music.
Although this type of music would seem very beautiful and soothing for you, don't try to talk down to kids when it comes to music. Just like any other things, talking down to them would often end up in failure. Allow them to appreciate it in their own, rather than forcing your ideals about it on them.
What can allow your children to appreciate classical music and listen to them more is by relating something with it. If you read stories to your kid, try playing related music in the background while reading the story. This can allow him/her to reminisce those special moments with you each time he/she hears similar music.
However, if you're going to relate music to stories, make sure that you play the same music when reading the same story to them. This can allow them to remember it more and be familiar with it. Also, make sure that you just don't pick out random songs to play while reading a story to your children. You should also make sure that the song that you'll play can relate to the mood of the story.