We went through that too and I use huggies and you have to tighten down the top good. Also make sure the flaps around the legs are set and pulled out so they aren't bunched up which helps a lot and blocks the leaks.

I noticed that a lot of the leaking happened with the band gaping in the front and once I realized I needed to tighten int down and make sure the size was right it was all better.

I also second the water proof pads. I have 8 sets of sheets for the crib and one water proof mattress cover. Works great.