Songs are fantastic and motivating resources for children.
We can difference between Nursery Rhymes, very good to practice language, and specific songs for teaching contents.

This is a great site with Nursery Rhymes

You can watch the videos with activities and coloring pages on the web http://www.mothergooseclub.com/ 

Or you can watch the videos through the official YouTube Channel https://www.youtube.com/user/MotherGooseClub 

One of the big problems we all face, whether teaching English to children or adults, is maintaining learners’ interest throughout our lessons. Consequently, we often have to be very creative in the techniques we use. What makes music such a great teaching tool is its universal appeal, connecting all cultures and languages. This makes it one of the best and most motivating resources in the classroom, regardless of the age or background of the learner.

This is the introduction of the article by Adam J.Simpson "How to use songs in the English language classroom". He gives tips about planning for the use of songs in class and he also points out "Six steps for making a song the focus of your class". Very useful to make your English lessons memorable for the students.

Another interesting site where you can find songs for teaching and much more is 

Here are some tips and ideas on how to use the LearnEnglish Kids website for listening practice with your classes.