Legal Question in Wills and Trusts in Pennsylvania

Don't do this on your own. There are many fomulations. You could say,

"I intentionally have chosen not to provide for my son, X, as I have made alternate provison for him outside of this will."

or

"I intentionally have chosen not to provide for my son, X, not out of lack of love and affection, but for my own personal reasons."

You could use any other phraseology. However, once you have passed on, it will be up to the court to try to interpret your will. To avoid any pitfalls, you want to make it clear to the court and anyone else reading your will that: (1) you were aware of your son's existence; (2) you intentionally or deliberately chose to exclude him as a beneficiary; and (3) you don't want to say anything defamatory or otherwise hurtful.

If you wish to leave everything to a minor (anyone under age 18 is a minor) then you need to create a testamentary trust.

Please, don't try and do this on your own. It would be best if you sat down with an estate planning attorney in your area to discuss your goals and make sure that a will is the right vehicle for you. Wills are not all that expensive. Failing that, then go to www.nolo.com or Legal Zoom or some other site (I am not recommending any of these but these sources are out there and you should use them at your own risk) and get a do-it-yourself will kit.