How to convince my mom and dad to get me a trampoline!?

see my mom and dad wont get me a trampoline because theres boys that come to my home sometimes cuz they r my neighbors, and if 1 come while we're not home they'll jump on it any break their arm. also I live in MA and we get alot of snow and cold weather, and my mom is like "well what will we do on snowy days about ur tramp.?" and of corse they cost alot but im a gymnast and I want one to practice flips and stuff. PLease answer and thanks!