Children can be introduced to Reiki, provided they really choose to do so freely. To please parents is not enough.

They must have a personal motivation, for example, to help overcome the stress at school,  treat cat or mom.

It is also imperative that parents agree and preferably at least one of them practice Reiki.

The lower age limit is around 7 years, because it is at this age that children begin to reason.
Must be taken into account that children are less able than adults to understand the reactions you can have with Reiki.

It is good for a child to be initiated for himself and that she/he practices in the circle of family and close friends.

Reiki is a precious gift and for the child to appreciate its true value, the child must make a personal contribution in exchange.

The "price" of course stands for something the child has of himself, DIY, craft, poem, song, etc. .. depending on their age.