The past two nights my 19 month old daughter has wet through her nappy during the night. They fit well and have been using the same brand since birth. She's been in this size for a few months. No change to how much she drinks or when.

Any idea why the sudden change? Any suggestions to stop it?

Edit: she's in size 5+ up to 36lb. She's 24lb at the minute. Would moving up a size not be huge on her?