You're not a terrible mum! I used to get upset too when my dd was little and acted like this (it's not just your children who misbehave - don't think that).
How did you handle it when they were kicking each other whilst you were talking to their mum?
How did you handle it when they ran off in the shop?
If you're leaving it until you get home to discipline them, i don't think it'll work as too much time will have passed by.
At home, i tried everything with my dd. Naughty step, confiscating toys, ignoring the bad and praising the good. Nothing worked! Luckily she's 5 now and is (most of the time) a little angel.
But, back then it was when were out and about that i struggled most with discipline. People would stop and stare whenever she went off on one, and i ended up feeling really embarrased, not reacting, and dd then felt as though she could get away with it.
So i sucked up my embarrasment. Each time she misbehaved outside, i found the nearest wall and told her to go and stand against it for five minutes (with me standing a few metres away). Each time she tried to run off, i'd put her back there until she got used to it. Basically, i treated the naughty wall outside as the same i would at home.
Yes, it caused a loooooot of passers-by to stop, stare and whisper, but i learned to not care.
Sorry for rambling. Just wanted you to know you're not alone, and this behaviour won't last forever.