I do not know where the biological father of my 6 year old daughter and 2 year old son is and haven't seen or heard from him in a year and a half.my husband wants to be their legal father and my daughter and son want that more than anything in the world.how do we go about doing this?

You get the biological father to sign a consent form, agreeing to the adoption. If you cannot find him the Court will issue an order that he can be served by publication. That means a specific newspaper (or newspapers) for a specific number of times with specific wording.

You must have exhausted all avenues of locating him before the Court will issue such an Order. Have you tried investigators to locate him?

Your 2-year old son understands what "adoption" means?

Also - what State?