|Did you try going to http://www.vistaprint.ca|
then choosing United States when you click on "Select a Country" in the top bar ?
If that doesn't work either....
"I am the parent - No luck - all other web addresses work but vistaprint."
then something is blocking you accessing that address.
Do you have a third party software firewall installed on the computer ?
Some anti-malware programs act like a software firewall - e.g. AdAware, Spybot.
In some cases there is one built into an anti-malware suite of programs - e.g.the paid version of AVG 2011.
In any of those cases....
If someone has answered Deny (or similar) when a message popped up regarding http://www.vistaprint.com that you answer Allow or Deny to, then it will be listed as a blocked address in the firewall or firewall like program somewhere - remove it from the list.