If it's only occasionally I don't think there is any harm! If you were doing it every day then that would be a bit odd..lol. but every once in a while I think is ok. Like a PP my mummy 'uniform' is trackies and a jumper during winter, DD is dressed in trackies and a jumper too, as she doesn't really have any other style of clothing, so we are dressed 'the same' but different colours/styles ITMS.