K.M.
My son does this too! I first noticed it in his car seat about a month ago when he was about 3 months old. He strains forward like he's trying to break out. And now he wiggles down as soon as I put him in the car seat to avoid the straps. In his swing, even though it's fully reclined, he leans forward, or leans towards the side. I just make sure he is always strapped in properly into the swing or car seat whenever I put him in those things. I also noticed that he doesn't really care for the swinging part so much anymore, so I put him in without swinging. In retrospect, I think this leaning behavior may have been a precursor to rolling over, which my son just learned how to do 2 weeks ago, at 4 months.