I suggest a few baby gates. Put one near the kitchen so they cant go in there alone. Or in a living room area so the can only play in one area. You could also get some safety latches, so they stay out of the cabinets. if you have things in the shower like razors you can buy a shower head caddy and keep all things up there out of their reach.
I agree with the previous post, baby proof and keep them within sight, as for the 4yo taking things from home, my 6Yo steals from walmart, anything he can hide in his shoes, pockets even in his underpants, i have taken away electronics, fav toys, and he gets spanked, he was getting so bad that i pretended to call 911, to ask them to take him to jail for stealing, i "asked" how many times a day they ate (1), that they cold showers, no toys or tv and kids in jail cant see their families until they are 10yo...it may sound extreme but it has worked
To be honest not really. I have a 9 yr old boy, 2 year old boy, 18 month daughter, and my next is due in June (boy). The best advice I can give you is extreme baby proofing. That is what I do. Such as every door has kid safety locks. Limits where they go. All knives are kept in a bin on a top shelf that they can no way reach. Cleaners are high up in laundry room, behind the locked door. Kitchen chairs I have put on top of the table so that they can't climb them. Not pretty but effective. I usually do baths together that way one isn'tgetting into things while I take care of the other. Extreme baby proofing is what keeps me sane. Hope this helps you