I would definitely get parents to take him to the dr for a check in case of infection. If it is not that, then is there anything that could be bothering him or making him nervous? Any changed either at home or at daycare? I had a 3 year old dcg who did that for a month or two when she first started with me and it turned out to be anxiety...the change of daycares and everything. Once she adjusted fully, she was fine.