The child would not pay Federal Estate Tax; your 50% value of the house would be in your estate; however, you have indicated that your estate will be below the exclusion, so no estate (inheritance) tax due.
The surviving tenant inherits your 50% of the house and gets a step up in basis equal to the fair market value of your 50% of the house. For example, if house was purchased for $100,000 and is worth $200,000 years down the line at date of death. Now, the basis of the asset in the hands of the surviving tenant is $150,000.
