Just planning ahead. Are 3 year olds good enough to be enrolled in taekwondo class?

I think yes. My godchild was enrolled in a karatedo class at 3 years old. You might want to check with the following if they accept three-year-old kids. https://www.facebook.com/donniegeislertaekwondo/ https://www.facebook.com/STEPMARTIALARTS/

I've seen a Facebook video of little kids practicing Taekwondo so maybe, yes. You can try enrolling your kid there. You may want to check first if s/he is willing to learn the art