Yes, I have made arrangements on matters relating to my children.

It is best to have your agreement for child support, visitation or other contact with a child, and/or distribution of property in the form of a notarized document. If you have a notarized document, it will be easier for you to go through the enforcement process in case of non-payment or not performing as agreed.
For more information on having your agreement notarized, you should consult your local notary public office. Click here for the website of the Japan National Notaries Association.