Doesa childhave inheritance rights?

First of all, did he have a Will?  If he did not then he died "intestate". This means that the intestacy laws of the state where he was domiciled as of the date of his death will control.  As a general rule in such a case, a surviving spouse will get 1/2 - 1/3 and the remaining children split 1/2 to 2/3 (your deceased brother's estate would get his share).

If your father had a Will, then you may or may not be entitled to a bequest depending on the terms of the Will. The fact is that a parent may disinherit their child; typically they have no automatic right to inherit from their parents.  Although generally, is such a situation, there should be specific disinheritance language in the Will to protect against an accidental disinheritance.  For example, if it appears the parent did not know about a child; or if the child was born after the Will was signed.  In such cases a child may have a right to “elect against the Will”; that is they have a right to certain assets. 

Additionally some assets can be transferred outside of probate.  For example, if your father had a small estate, property may have been transferred by affidavit or otherwise.  Further, some assets may have been held as "joint tenants with right of survivorship", in which case the other joint tenant would have received your father's share to property operation of law.  Also, funds in an IRA, pension, 401(k), or other retirement plan by-pass probate and go directly to the designated beneficiaries.  The same holds true for any life insurance proceeds.

At this point you speak witl speak with a probate attorney. You can make an intestacy claim to the estate; if there is an objection because he in fact had a Will, then your stepmother will have to produce it. You can then see what you were or were not left.