Every year on June 1st the plan year for the Child Allowance benefit changes over.
To renew your Child Allowance you need to send in a genkyo todoke, a form that notifies the authorities that you are still eligible for the benefit.
You will not receive the benefit for the 2017 year (6/2017 – 5/2018) unless you do this.
The necessary forms should be sent to your house in early June, so watch for them and get yours in early.
(Contact information and details concerning this can be found at the following City website:) http://www.city.kawasaki.jp/450/page/0000030462.html