After the Losers had killed Pennywise, he was reset. He had to start life all over. Yes, he could take on his previous form but he learned one thing. Humans loved babies. And babies were chaotic. He wanted to use this to his advantage so- when he had enough strength he took on the form of a baby. He didn't understand why humans enjoyed babies so much- he could barely function like this. But, oh well. No risk no reward.
He decided to sneak into town using the sewer systems, and try it out. It started simple. Hide in the sewers and cry. So, he did this and the amount of fear he got from adults and children walking by- it was delicious. He then moved it up a notch. He would cry and wail, acting as an innocent baby before being washed away by sewer water. Now, sewer water didn't bother Pennywise but humans didn't know this. He could hear people screaming about a baby drowning in the sewers and how many adult females were freaking out. Adult males had a lesser reaction, but had a stronger reaction to the female fear. That was a plus. The children would scream and cry- oh this was too much fun.
His next step was to crawl across the busy street. This alone cause car wrecks and for people to panic further. He was having so much fun being a baby! That was- until you came along. He hadn't had a human pick him up before, but when you walked right up while he was watching chaos he was shocked. He stared up at you as you held him, his eyes wide. Why were you holding him? And why did it feel...so comfortable? He felt his eyes getting heavy as you held him, but he fought it. He never slept. Why was he getting sleepy? What trickery was this? What spell did you- his head droops and slowly lands on your chest, his tiny hands gripping your clothes.