FAQ

Their force-feeding of the potion does not appear to hurt Hercules. However, he did cry when the rubber nipple was forcefully taken out of his mouth.

No one knows for sure. It can be speculated that if the baby sucked on it then the spikes on the nipple would have hurt his mouth by pricking his gums and tongue.

While not explained in the movie, there could be interpretations that Hades was too busy or ignorant to know about the life status of Hercules. After hearing the news report from his minions Pain and Panic, he would presumably be much calmer to wait for the day he could finally release the titans his brother Zeus had imprisoned.