We are InChrist which means we are in His HolySpirit. It is His HolySpirit in us and us in His HolySpirit that makes us His child.
In the KJV the term SpiritOfGod and then SpiritOfChrist is used interchangeably. This means that the SpiritOfGod is the SpiritOfChrist and we know that there is only One Spirit Eph 4:4 1Co 12:13 1Co 6:17.