When I was little opening cans was definitely a challenge for me. My little sister who was about six or seven years old at the time always had to show me how or she would do it herself. The next day I would have to open a can and I would have no idea how even though my little sister had shown me how to open a can just the day before.
Realizing you cannot open something as simple as a can should be a sign that a special needs child needs Occupational Therapy to aid in strengthening their motor skills.
Parents, if your child is struggling with opening cans or other motor skill related activities then the one thing you should do is show them how to do it, explain the process to them and work on it with them constantly until you are positive they have the concept down and that they know how to do it completely.