Well, there is a difference between not expecting gifts & not wanting them.
My kids have too much stuff all ready. We put "NO GIFTS PLEASE" on our invitations because we really don't want the guest kids to bring any. Sometimes they still do - but it's more along the lines of balloons than toys. And we get LOTS of home-made cards, which is sweet.
We do NOT open any gifts OR cards during the party, regardless. We wait until all of the kids have gone home and we open them after the last guest has left. It makes a nice party-ending for our kiddos - no big let down. And if family members want to stay for gift opening, that's fine. We do make sure there will be gifts to open - but they are from us & extended family - not the invited playmates.
Now, if you don't CARE if you get gifts, your wording is fine. If you don't want them, be explicit.
And I have found that people don't expect a meal at a party unless it's at meal time and they're told there will be pizza or a cook-out. Snacks (like chips) are fine.
And I agree w/ everyone who said 2 weeks.