DD1's been reliably toilet trained for past 7 months. Started nursery in Sept, only had one accident all term. Over Christmas though, she's started having an accident most days - some more accidental than others - she sometimes genuinely doesn't make it to the loo on time (not always at times when she's especially excited/absorbed, either), but at other times she seems to just stand there and wee on the floor deliberately. On one occasion she weed because she'd kept fibbing about needing the toilet as a way of getting off the naughty step and I decided to risk leaving her there - then the following day she sat herself down on the step and weed spontaneously.
She still wears a nappy at night, and the last few days this 'regression' has extended to pooing in the nappy before going to bed and on waking in the morning - this is 100% deliberate and she thinks it's very funny.
So far we've mostly been ignoring all this, hoping it's one of those silly phases that'll evaporate of its own accord. I'm hoping the start of term on Mon might get things back to normal, but am a bit concerned that if it doesn't, she's going to start weeing on the floor at nursery on a regular basis which would be very tiresome.
There haven't been any major life events that I can think of - no new baby, house move or anything. DD2 is 16 months and close to walking; DD1's behaviour towards her (and in fact her behaviour in general) had been pretty bad lately but in fact has been improving as the toilet habits worsen.
The only theory I can come up with is that as she gets slowly and reluctantly more disciplined in her behaviour, she's hit on this as the one area of her life that she - and only she - really can have control of. This doesn't help me solve it though!