I'm going to gamble that this advice is going to be totally slammed by you youngsters but, DO NOT teach your kids sign language in lieu of letting them learn to speak normally. Somewhere in the early millennial round of parents, someone got the cockamamie idea that kids grow up better if they don't have to be frustrated learning how to speak. Frustration is also known as facing an obstacle and learning to overcome it. It's part of life.
You can thank me later after you save money on speech therapists.