SEATTLE — Chris Pratt has opened up about his son’s premature birth while sharing his experience visiting a children’s hospital.

The actor posted photos on Instagram from his visit Monday to Seattle Children’s Hospital. He showed off a picture of him with a set of premature twins. He writes that ever since his son Jack’s birth, he has “a special affinity for the NICU (neo-natal intensive care unit).”

Pratt’s wife, actress Anna Faris, gave birth to Jack in August 2012.

Pratt also shared pictures of him with a cancer patient and another child at the hospital. He thanked the facility for “the opportunity to come by and brighten some days,” adding, “My heart is full.”

Pratt has appeared in the TV series “Parks and Recreation” and the film “Guardians of the Galaxy.”