I am a widow or widower TEI family member. Can I enroll my TEI child who is a TEI family member without enrolling myself in FEDVIP?

No. A widow or widower who is a TEI family member is the TEI certifying family member. Because there is no available sponsor, you are the enrollee, and must either: (a) Enroll yourself and the TEI child in a self plus one enrollment; or (b) Enroll all TEI family members in a self and family enrollment, in order for the TEI child to receive FEDVIP coverage.