IPC clearly provides in its General exceptions the law relating to infancy. It states that any person less than 7 years of age cannot be held liable for the crime committed. The reason  being he cannot have the required mens rea. However if an elder person uses the child for committing any offence, the elder person will be held liable fully but the child will be set free.

Section 82 in The Indian Penal Code

82. Act of a child under seven years of age.—Nothing is an offence which is done by a child under seven years of age.

hi

first of all if a child below 7 yeras commit a crime is not liable as per the settled law principles. But still there is a catch in this situation the court may look out the crime scenerio and incidences happen one after another accordingly court may find out the the menatl developmnet of the child. If court is of the opinion that the child cannot develop such an intention to commit or plan the series of said crime then it will pass order in favor of the child and let him/her set free.