If my kid/s decide tennis is the sport for them, then great. But I doubt they'll be coached by me. I'll happily drive them around to training and tournaments and hit with them (if that's what they want to do), but I want my relationship to "dad" not "coach-dad"!
That said, I can only think of maybe 3 or 4 coaches I would trust to do a really high quality job (out of the maybe hundreds of coaches I know and have met!) - could be hard for the coach as well, knowing that dad is national coach (no pressure there then!)
Think I'd like my son/daughter to play rugby, but anything they enjoy will do as long as it's not football!