There are lots of programs and string camps for kids but this article from string magazine gathers 7 different programs which can help to improve your playing as an adult. 

I like number 3, Kneisel Hall’s Adult Chamber Music Institute best as it is so hard to find a group of musicians to better your chamber experience and playing.  And this provides the excellent opportunity to learn and expand your repertoire at the same time, a chance to meet likeminded musicians all in the love of music.  Do read on here!