Children's expressions of positive emotion are sustained by smiling, touching, and playing with parents and siblings: A naturalistic observational study of family life
Developmental Psychology (2016) - Comment
pubmed: 26524382  doi: 10.1037/a0039854  issn: 1939-0599  issn: 0012-1649 

Sunhye Bai, Rena L. Repetti, Jacqueline B. Sperling