ZenWorld

I am on the side with the hotel here, but let me explain the reasons:

1. When hotels implement any policies, they must consider the pros and cons - and in this case, they may lose out on certain families - like yours, but in return, they retain business of people who wanted a quiet lounge; in the case of Novotel Singapore, they have a lot of business travelers who wanted a quiet lounge.

2. While you mentioned your kid is well-behaved, but I am sure you have also come across many badly behaved kids, but their parents think they are angels anyway. A couple of tantrum thrown in the lounge does not make the kids badly behaved in their opinion, but from the perspective of the rest of the guests, it is awful manners.
(That is not to say your kid is badly behaved. But from the Hotel's perspective, they have no idea as each kid is different, and they cannot afford the risk if they want to maintain the lounge's standards in terms of exclusivity, peace and quietness. )

3. Once they admit younger kids, where do they draw the line with behaviour? It is harder to kick kids out when they are in, then stopping it with minimum age from the start. (If they admit your kid, they have to admit all kids, including badly behaved ones, because no one knows when the little ones will show their ugly side, if any.)

4. Kudos the hotel for consistency; they did not target only 1 family, but doing it consistently. It means they are not just unfair to you; they have considered the potential business loss of families with young kids.

5. While they stopped your kid, they tried their best with alternative arrangements. Breakfast at restaurant, drinks at Lobby Bar, etc. They could have easily not done that for you. Add the willingness to shift your stay by a night for your booking mistake, I think they have done well.

I can understand your frustrations, and from your angle, it appears really unfair, but looking at the bigger picture, especially when your kid is older (>12), and you revisit the hotel and lounge again, there will be no loud crying little kids, running amok in the lounge, and that is something to enjoy then.

Sorry that the stay was not so good for your family due to the lounge policies, but I guess that is something to plan and consider in your future family travels. From the other side of the coin, I am with the hotel, at least in the consistency of the lounge policy execution, and also their attempts to make up to you in other ways.