KAWAIIIIII! (kah-wah-eeeeeeeee) Cute. Used as an exclamation by 98% of the Japanese women of any age when they see your kid.
Hana ga takai! (hah-nah gah tah-kai) What a big nose!
O-tosan ni sokkuri! (oh-toe-sahn nee soak-curry) She look just like her father! Used by the other, crueler 2%.
Ningyo mitai! (neen-gyoh me-tie) She looks like a doll!
Responses I've thought of, but have not deployed, when a stranger demands to play with your doll:
SARS wa utsuru kamo kedo, doozo. (SARS wah oo-tsoo-roo kaw-moe keh-doe, doe-zoe) Her SARS might be contagious, but sure, go ahead.
Mokuyoubi made ni kaeshite ne. (mow-coup-yo-bee mah-day nee kai-eh-shtay nay) Just bring her back by Thursday.
500-en (go-hya-koo-en) 500 yen. (Actually, I use that one all the time.)