I pinned a zombie near my fenced-in villagers and the babies kept running into the enclosure before I could get more blocks. They would run directly to the zombie and sit next to it for no apparent reason. I stepped away from my computer and one was turned into a zombie and killed the rest of the villagers (save one which promptly died right in front of me). I turned on LAN mode to access cheats and check for glitched mobs or blocks where they may have escaped or the hitboxes may have overlapped but didn't see anything unusual. I tried it again with a spawn egg and sure enough the baby villagers would stay RIGHT next to the zombie? maybe because of the boat it's stuck in? I've never seen a villager pathfind towards an enemy in an enclosed space with no doors to try and escape through.