My DS is now 14 months old and for about the last 6-8 weeks, nearly every morning when I go in to him in the morning his nappy has leaked around the waistband, through his vest and normally his pj's are wet too (and sometimes the sleeping bag as well).
This has started around the same time that we moved from size 4+ to size 5 nappies. In the past when his night-time nappy had leaked we moved up a size and this seemed to solve the problem.
In the past I have also used cotton wool pads (the large oval ones) inside the nappy under where the tabs do up to absorb any leaks that way.
So any helpful hints or ideas are welcome in an attempt to reduce the washing pile. We use Pampers baby-dry 12 hour proper night time expensive nappies.