DD1 was an "absolute delight" and the "most enjoyable little girl" to her carers - they didn't think she ever cried, talked back, threw tantrums etc. They didn't believe me me when I told them that she did this at home! Until one day...... she had a massive meltdown at CC when she was 3.5y and apparently everyone was shocked. They were asking the carer what she ahd done to DD1 and what on earth had happened. I had to reassure them that this was actually fairly normal and not to be concerned

DD2 was awful Monday morning and was whingy, clingy, sooky and temperamental - until she got to CC and she was happy for the whole day

So yes, they can turn it on at CC and be sweet and charming and well behaved and then become completely the opposite at home. I think I would prefer it that was to the other way around though...