Ay, iba-iba talaga ang bawat baby kaya 3-5 times a day for your 18-month-old could be normal especially if she's eating lots of fruits, veggies, or milk, a few of my mum friends' toddlers din ganitong frequency! As long as the poop is soft but formed (not watery/diarrhea) and your little one seems happy, energetic, and gaining weight okay, walang problema usually. But kung concerned ka or if suddenly naging frequent ito or may other changes like blood sa stool or she seems uncomfortable, better check with your pedia just to be sure, ha?