D.S.
I haven't read the other posts but have found that if I start off the day with 30min of PLAY - totally doing whatever THEY are interested in, not leading them in a project but actually following their lead in play - this inspires better behavior than any reward or punishment system. I end the day with this too.
You likely feel you are already playing with them all day - but this is child-led play and for 30min straight without any interruptions - not phone, email, laundry, dishes - I will admit I find it drastically boring ("yes, I'll be the baby when we play family" - argh!) but also their little eyes shine more with happiness and their behavior is better when we do this.
Good luck,
D.