I enjoy playing piano(although it can become a bit tedious) and I think that it is a good activity for children because it helps them improve their fine motor skills and hand eye coordination. It is also a good way to introduce your child to the world of music.
It is also worth noting that it can be difficult to make someone practice for 30-60 minutes while sitting still on a hard wooden bench especially if that someone is 5 years old. Another benefit of piano that I have noticed is that it tends to help relive stress and helps me calm down. Pianos do tend to be rather expensive though, so don’t buy one unless you are absolutely shure that you want to learn to play.