Q 老师好：

I want to go playing baseball.

可知go+运动Ving；但若要表达弹奏乐器

I want to go to play(playing) the piano.→该用to V还是Ving呢?

http://www/uc/myshow/blog/misc/gif/E___6726EN00SIGG.gif不可说：

I want to go playing baseball.

go 之后若接 V-ing 时，多由单一动词转化而成，如：

Let’s go fishing / hunting / jogging / shopping / swimming…

因此，你的句子应改成：

I want to play baseball. Would you like to join me?

或：

Let’s go (and) play baseball. (and 可省略)

同理，不可说：

I want to go playing the piano.

应说：

I want to play the piano.

或：

Let’s go (and) play the piano.