Abnormal for 6.5 m.o to tuck thumbs in fists intermittently? Grasps and transfers objects appropriately and otherwise has reached milestones on time

From birth-8 weeks, . intermittent " cortical thumbs" can be normal Fine motor skills at 6 ½ -7 mos. = "raking " a pellet into the palm with the index finger, a "scissors" grasp to pick up small objects between the thumb & index finger & self-feeding crackers. Prenatal risk factors for CP + abnormal neurological exam or parental concern warrant assessment by WI's Early Intervention Program. Call (800) 642-7837. .
Likely normal. it is normal if it is intermittent. you can help this by use proper toys to hold in his hands and massage and stretch the joint gentlly. also if both hand does the same it is more reassuring.