Children need to be taught how to perform chores just the way they're taught to walk and dress themselves. If you want your older child to clean the toaster, explain that it will have to be unplugged as a safety precaution. Show him how to open the crumb door. Discuss the most efficient way to dispose of the crumbs, like on a paper towel or in the sink. Supervise him the first time or two or until you're confident he knows the best and safest way to do the job.
Once you have a level of confidence that he can do the task, give him ownership of it and be consistent. Don't get frustrated and do the job yourself. Don't yell. If he forgets more than a couple of times, provide him with a chore calendar, and give him the task of planning out his chores ahead of time. When your child does perform a chore correctly and on time, praise him and let him know you appreciate his help. All kids, young and older, want to feel capable, needed and appreciated -- even when it comes to cleaning.