All children are smart enough to learn chess and to become very good. There are three things that prevent them from being good. First is no exposure and not enough exposure to chess. Second, some people don't like chess or any games in nature. And third is, whether they are willing to do the hard work.
For the first obstacle, as parents, you should provide your child enough exposure to chess. Don't choose for them, but let them choose their activities. If they don't like it at all after multiple tries, then switch to other activities they like.
For second, even someone who don't like chess that much can become very good with hard work. The second Polgar sister Sofia is a proof. She loves art much more than chess, and she nontheless became an IM.
The third one is critical for anyone engaging in any endeavor. If you want to be successful, you have to pay with your hard work.