Aww, saan exactly ang pantal na bilog na yan, sa baby mo or sa iyo? Kasi maraming possibilities, pwedeng milia (tiny white bumps), heat rash, fungal infection, or kahit dermatitis lang, lalo na ngayon sobrang init at humid. I'd really suggest taking a photo and showing it to your pedia or dermatologist asap para ma-identify exactly kung ano siya, kasi depende ang treatment, some go away on their own, iba need ng cream or medicine. One of my mum friends had something similar sa baby niya and it turned out to be nothing serious, pero mas peace of mind kami when the doc confirmed it. Hugs, I know nakaka-alala talaga pag may sudden rash or marks!