Could he be teething? I recall my DS started to wake around that age with teeth troubles - although a quick visit wouldn't remedy the situation so maybe it's not that......sorry not much help here! Also, try to do what you did with your first child as he may be expecting a visit for a little grizzle when really he might be able to self settle - it may not wake your toddler after all (or your toddler might be easier to resettle if it does). I think a second born cild can be responded to more quickly for that very reason but this could set up a pattern of waking and expecting you there.