It is a very effective object lesson and one that children will remember. Sometimes people want to make a tag for those around them, and they give people a name like, naughty, or stupid, or thief, and this name is often based on one small incident. This is not what God wants us to do.
Nobody is perfect.
The String - This also needs to be removed carefully. Many people become too attached to something on earth. Some people tell lies, so many that they are not sure of the truth any more. Some people become very attached to alcohol or drugs, so attached that they cannot live without it. Some people become attached to eating food, or not eating food.