Leaky Cushie - what am I doing wrong??

[Tanstar]

I'm wondering if there is a way to make them smaller? I noticed the snaps on the inside so if I fold the front down in front of him they are exposed but then it's too tight on his buddha belly? The wee he did went all over his clothes to the side and back and when I took the nappy off it was dry on the outside so I can't even figure out how or where it leaked...Im guessing maybe around the leg???? Ugh so clueless and I love the Cushie fabric so want to try and get it right!