To get life insurance, insurance companies, want to see an "insurable interest" between the person being insured for life insurance and the owner of the life insurance policy who is purchasing the coverage.
Since he is the father of your child, you have an insurable interest on him.
The parents of a child have an insurable interest in each other since one would be financially impacted by the death of the other.
Usually, a life insurance carrier will require the permission/approval of the insured person in order for someone else to buy life insurance on that person.
Learn how to buy life insurance online