This is a lovely little ESL warmer for kids which will immediately pique their interest in your class. It will get their sensory juices flowing and is particularly useful as a warmer if you've been teaching classroom objects, household items, fruits and vegetables, animals, shapes, toys, all common topics in young learner English textbooks.
For this introduction, let's assume you've been learning classroom objects. Go round your home, the office or teacher's room and get hold of some common classroom objects, pen, pencil, rubber, ruler, paper, pencil sharpener, pencil case, etc. Put them all in a bag and bring the bag to class.
At the start of your class, put your students into pairs. Now walk around the class and invite every student to dip their hand into the bag to feel inside (they aren't allowed to peek inside the bag). Give each student just 5-10 seconds to feel inside and then move to the next student. Give every child a chance to feel inside the bag.
At the end, tell your pairs that they must work together to name all of the things they could feel in the bag. Give them a minute or so to discuss. Now ask each pair to name one thing they could feel in the bag. One student from each pair should then come and write the word on the board (you can help them with spelling, if needed, or ask them to bring their book to help).
Go around each pair until you have covered all the items in the bag. To finish, tip out the bag and go through the items again.
You can do this activity with fruits and vegetables, household objects, toys, shapes, animals (if you have small models), whatever really. This warmer will get your kids speaking and interacting quickly.