... Ever since Preschool, per my daughter, (she is now on 3rd Grade), it has been the Teachers "RULE"... that party invitations are given to the Teacher first... to disperse. So that.... it does not disrupt class or class time.... and is usually given at a time that is best for the class. PER the Teacher. Usually, before school lets out.
For RSVP's.... most all parents I know... leave a phone contact number AND an e-mail address. That is... most convenient, for parents.
Not all parents, can leave a note in the cubby... or in their take home folder. They are at work. Therefore, leave a phone contact number AND an e-mail address, for them to contact/RSVP you. Directly.
That is what I would do. I would not, personally... make a paper RSVP... for the parents to leave for you... and a child that young... cannot be counted on to do it for the parent... and leave it in your daughter's cubby. THEN, what if it gets lost? Which does happen. And/or the child will even FORGET to give it, to your daughter or her cubby. Then the Teacher.. has to 'help' find it etc. THAT has happened... before... in my daughter's classes. It is.... not reliable.
Most invitations, per myself and other parents... have dispersed invitations even 1 month... PRIOR to the birthday, date. Because, parents are busy.... and their children have weekend classes/activities/obligations too.
So for me, personally, I would disperse the invitations... earlier.... not 1.5 weeks prior to the birthday party, date.
AND put the birthday "RSVP by" date on it.... AND the party's start and end, time. So it is defined.... because parents, per their hectic-ness... need to know when a party is ended.
ALSO... you need to specify... IF it is a "drop-off" party... OR if the parents can stay... so THEN.. you need to ask, on the invitation... HOW MANY parents will also be attending with their child.
THEN, that will also, impact your party/headcount/food you need to provide... and accommodations....
all the best,
Susan