don't beat kids when you are mad, then spoil them when you are g

your kinds need discipline, not abuse. yes, you abused them, don't find excuse for your behavior; yes, your kids will remember it all their lives. I have a good friend, know her since baby, perfect family for me, like her mom too. but when we grow up and both in US, she told me her mom used to beat her when she was young for some small things. she is in her 40th, and she still remembers it. now, if she is too mad with her own kids, she will time out herself in another room, so she won't beat them as what her mom did. you should try this first, or ask your LG to take care of the kids when you are out of control.
Hate to write so long, but i think you need help seriously, just some of my suggestions:
1. ask yourselves, why they did it? eg., pour the shampoo, if she just wants playingbubbles like most kids. you should tell her it is wrong to use shampoo, and take her to the shop and buy a bubble solutions for blowing, or a bubble bath solution, and have a bubble bath. you can even show her how to make your own solution by only use several drops of shampoo(or detergent, soap) in a bucket. if they are just bored, then you may need to find more things for them to do: play outside more, go the liberary, join play group... most important, find out what bother you the most, and is that really matters?
2.if you dislike something so much and will not tolarete. think first,get a list, and talk to your kids when both of you are calm and happy. you need to teach them discipline. first tell them which behaviors are not allowed in the home. give a short explaination, esp. don't empty shampoo bottle, because shampoo is for washing mom's and your hair, not for play. then tell them the consequence for break the rules: first time, time out minute=age; second time, add a minute or two; third time, lose a previlage. you need to decide what is the previlage thing together.
3.stick to your rules. you must stick to them, esp. at the first several months. this way, they will learn that you mean it. make sure your LG does the same. if they break it, no screaming, no beating,no nagging, stand in front of them, count 1, then send her to your time out place. if she makes a fuss, she will be timed out in her room alone. same for the other times. if she is fussy and you need her to stop, you can follow the 1,2,3 rules. you ask her to stop, if not, you just count 1, then 2, then 3. then she is going to get time out... if you stick to it, it will work after a while, and your kids will test you for sure. but don't scream, beat,and argue with them, just punish them as you decide together.
4. award good behavior. when you make the rules, make sure you have rewards for good behaviors. get a canlendar, tell your kids, you will write down their behaviors each day together before sleep.if there is no time out of the day, they can put their faviorate sticker on that day, or if they help mom or do some great things, they can get an extra sticker for the day. if they get # stickers, they get a reward. decide your reward together, you will be suprised what they want. my son's faviorate reward was playing board game with me. encourage their good behaviors as much as you can, that is the most important part of the discipline. they are punished because of breaking the rules, not because mom is mad; they are rewarded because of good behaviors, not because mom is happy.