My daughter is going on 8 months (although was 8+wks early) and rarely laughs. We'll maybe catch a giggle a few times per week. She is constantly smiling and chatting though and we did ask the pediatrician and neonatologist as well as the occupational therapist. None thought it was a problem. I don't think she even started laughing until at least six months which was nerve racking for us in itself.