I would sing the song for him while pointing to each picture in order. When I got to the blank box, I asked him to pick a picture and place it on the box. If it was difficult to choose the correct item, I asked him to sing along with me and many times he would automatically insert the name of the correct item! The melody and/or rhythm would assist him in determining the missing item.
I've given the example above using fruit. You can actually make strips using different groups such as colors, numbers, vegetables, animals, etc. I enjoy using pictures of musical instruments!
The sequences can be as easy or difficult as needed. By changing the number, order and placement of pictures, you can make a sequence that meets your childs needs!
If you would like musical sequences and picture cards, click on the Activity Download tab at the top of the page and them look for Sequencing Activity Download. The download includes pdf's of 5 sequences and pictures of instruments. I like to laminate each sequence and even the individual instrument cards to make them last longer!