When you first teach the rhyme during circle time, you can work with a book that has pictures along with the rhyme, or create your own flannel board pictures for the presentation. You may want to teach it first in verse and then have the children learn to sing the song. Expand the discussion by asking what would happen if other animals were to follow her to school. Talk about appropriate school behavior and rules during your discussion. If you are presenting on multiple days, you can use a book one day and do the flannel presentation another day. Help the children memorize the rhyme one day and teach the song later in the week. Engage a different aspect of the discussion each day of the presentation.
One craft to do in conjunction with "Mary Had a Little Lamb" is to have the children glue cotton balls onto pictures of the lamb. Have a small pot of glue accessible to each child and let them dip their cotton balls and then place them. Or you can apply the glue to the paper and allow the children to place cotton balls on the dots. This is a great tactile activity, which allows you to discuss the feelings of soft and smooth. In addition, you could to create the schoolhouse or have the children color a picture of Mary and the little lamb. Or have the students paint the scene or draw their own picture of it.
Extend the activity to pretend play by having the children act out the nursery rhyme. Assign one child to be Mary and another to be the lamb. You can have a few students be schoolchildren and one student be the teacher and act out the second verse of the poem as well. Include more children in the presentation by adding extra verses with other animals in them. This would make a good parents' day activity. To expand the program, you could include additional nursery rhymes, to create more parts for other children.