There are demons who never had a physical body of their own and there are impure spirits who had a physical body and went astray.
Often there are both in/around the same person. Believe what you want to believe, but if your loved one dies and their soul hangs around after they leave their physical body to help surviving children or family, their soul does not become a demon.
If we are in a physical body, we are sinners and impure. Spiritual growth and God’s Grace lifts us out of impurity.
Children are created pure, thus we must become like them to know God.
I have helped many, many souls of abortions cross over as they were hanging on to their mothers. They were pure but lost and needed guidance to go home. They were not demons just because they were spirits or souls without a physical body.
Nothing scriptural about what you just posted. When the body dies, the soul is in the presence of the Lord (2 Cor 5:6). There is nothing in scripture indicating the God allows the soul to wander around after death. Jewish tradition was that the soul stayed near the dead body for up to a week after death, but that has no basis in scripture either.
Children are created pure, thus we must become like them to know God.
The context that Christ used in being as a child in order to enter the Kingdom of Heaven is that we must be as accepting as children, without doubt, trusting in Christ alone.