This is such a big responsibility that it explains why some people remain childless and raise tropical fish instead. Watch using Nintendo as a babysitter. While it may be an effort, there is no substitute for your direct involvement with your kids. Factor in the use of Nintendo as childcare at limited times, so that you have control. The hour after you get home from work may be the exception that proves this rule.
All good games have a compulsive nature.
When you notice that your child has not eaten or slept for days, a trip to the fusebox to manufacture a power outage is in order. Talk to your kid and start thinking of diversionary tactics. Talk about Nintendo use with your child. Become conversant in Nintendo-ese. Try to inject your concerns without polarizing the argument.