$$$ strapped dilemma: give baby stuff to preg-lil-sis or sell it to keep up with my own growing baby?

I recently had a baby and have some nice baby stuff (walker, crib, portable crib, glider, activity mat, swing, jumper, bouncer, bedding sets, stoller and matching car seat). My immature jobless 20 year old sister is having a baby in Feb. and she and bbdaddy (who barely works) think raising a baby is going to be easy. Hubby and I work hard but money doesn't come easy. I don't know if they expect me to give them MY baby stuff. I want to sell my stuff on my local craigslist so I can keep up with my growing infant and what she needs. Will I seem like a jerk? We haven't talked about this at all and I am afraid to bring it up. What should I do and say?