We only just took our baby gates down, last summer, when DS2 learnt to climb over them at the ripe old age of 7. We now have a 4' tall dog gate to keep him out of the kitchen and bathroom, unsupervised. Soon after learning to climb, he mastered undoing things, so the handle of the dog gate is now secured with a removable cable tie, much to DS1's disgust.
DS1's prescription medication for his ADHD is kept in a cash box with a combination lock. He's 10 and we don't want him to decide to be grown up and take it upon himself to take his own medicine.
Things that need to be kept safe are either in the kitchen or locked in our bedroom, which also has a keypad lock. This means that we can also keep the key in the window lock in there, so we have a sort of fire escape, without worrying about one of the boys opening it, during the day.
The child lock is enabled on the washer, as DS2 went through a phase of tampering with it when he was in the kitchen.
We have an induction hob - they don't stay hot for very long, when you've finished with them.
The TV cabinet is lockable, as are any cupboards where we keep toys with small bits and the boys' wardrobe. The cupboard under the stairs has also been kept locked since DS2 started going in there and dismantling the vacuum cleaner.
We did consider replacing the old carpet with hard flooring, for easy cleaning, but the carpet is acoustically a lot more gentle, so we've stuck with it and invested in a good carpet washer.