im 15, well almost 16 and i wanna work out, but my parents wont let me because apparently it wont let me grow as tall as i should, so first at all .. is it true?
and second... what kind of light exercises can i do to build some muscle ,i already do a lot of push-ups pull-ups sit-ups but kinda lost effect

Physical activity won't stunt your growth. In fact, it's good to produce bone mass.
The exercises you do now sound great. If you want to add some exercises that will be great for you and are guaranteed not to harm your growth, add yoga to your routine. I loved doing yoga when I was a teen because it helped with all the stress that every teenager goes through.

I am 16 and I work out a lot, my parents thought the same thing, but i am 5'8 and when i started working out i was only 5'4, so i dont think its true that it stunts growth, excercise is so good for the body and if you want to do it, you always should
p.s. i do push ups, pull ups, sit ups, i run in place and i use 5 to 10 pound weights for lifting. I have developed lots of muscle since i have used weights.