We've been incorporating tennis practice into our daily homeschool schedule lately. The weather has been so nice that even on days when it rains there is still a little time in the morning or evening to play.
Today I let Gloria practice returning the ball until we'd gone through the whole bag of balls (which I found in the garage), and then we gathered them all up and she got to practice serving until she went through the bag again. Then Danya got to do the same thing.
They are both getting better by leaps and bounds. I can already imagine how they'll be playing a few years from now after spending every summer practicing with their siblings and their dad and I for a half hour or more almost every day. We also include anyone who wanders into the tennis courts while we're playing, if they want to play. We've always got extra rackets and balls with us just in case.