DD (just 5) and DS (2) are going through an awful phase of winding each other up. Obviously it's exacerbated by it being half term and DD being around more but even in term time the time between 3pm and bedtime is very challenging.
DS is endlessly fascinated with all DD's things (and she has a lot of them!) ornaments, hair accessories, craft stuff etc. She is patient for a very short time until he inevitably breaks or messes up something. I try to get her to keep her 'special' things out of his reach but he is very determined and will usually find a way to get to them. Also, she doesn't want to do crafts shut away from everyone else. Also have the issue that anything he touches immediately becomes precious to her even if it wasn't before.
They are ok with constant supervision and refereeing but this makes it impossible for me to do anything else (even thinking is tricky) and it's obviously not healthy for me to be constantly mediating.
They are better outside than in but DS is very reckless and needs careful supervision in garden too. Playdates are a nightmare as they are usually with DD's friends so DS just has even more 'stuff' to try to mess up!
DD is pretty highly strung and easily wound up. DS is very active and physical.
I'm sure this is a very common problem but none of my friends seem to have the same age / gender / personality dynamic so I don't have anyone in real life to turn to for advice.