Discipline means "teaching", not punishment, so while you can't do anything resembling punishment yet (good cos it's not nice at any age, you've got a while before you have to be the meanie!) you can do lots of teaching. A lot of it is about communicating in a way they understand.
- Chucked food on the floor
> Take food away, they're obviously finished. You don't need to comment even but they understand that food on the floor = mealtime over. You can offer the food again later if they are still hungry but make it clear no messing around.
- Refused to sit in the highchair
> Could you try a little table and chair for toddlers? Or try moving the mealtime, it might be she's too hungry/not hungry enough.
- Chucked all the toys and water out of the bath on to the floor
> Keep baths quick, perhaps look into trying showers soon?
- Refused to get in the bath
> Sequencing can help, so she understands in advance there's going to be a bath and then after the bath something nice like a story.
- Refused to get nappy changed
> Hmm I think I had to sit on DS and be very very quick!