It's not your call to make regarding if your child makes it as a professional singer. Your child might be judged by certain people who are professionals. These people would determine if your child can realistically make it as a professional singer. If your child can sing a song by someone who is famous in the music industry, and if other people can see, and listen to your child sing, then maybe someday someone who is famous will vouch, for your child if your child does have talent.
I recommend, for you to make a video of your child singing a song that he, or she learned by a famous singer, and then you should post it online. You can try uploading it on youtube, and then you can see, for yourself what people say about your child. If this is one of your child's dreams, then I don't see why he, or she can't try to pursue it.
The song that your child chooses should be similar to his, or her voice, and this might intrigue people!
I don't know if your child can realistically become a professional singer, and I have no idea why you think your child can't become a professional singer.
Perhaps later down the road, your child might compose his, or her own songs, and he, or she might make it BIG!!!