The OP has posted 7 times using words. At no point has she answered questions about the wording of the invite or poll. What she has actually said is:
We invited his whole class to his birthday party through the class WhatsApp group.
There is a clear difference between “Little Jonny will be having a birthday party at JumpWorld at 3pm on Saturday 11th” (information) and “you’re all invited to…….” (Invitation)
12 did say they could make it, (I did a poll) because not many really responded to the invite.
Suggests the OP’s invitation may have been unclear.
I sent the invite and then a follow up poll a week later.
OP hasn’t shared the wording of the poll, and this seems a weird way to collect RSVPs. “Can you come?” is different to “will you come?”
assumed if 12 had put yes we can attend and knew the date and time they would just show up.
Can attend, not will attend. Interesting wording by the OP. Perhaps she wasn’t clear on WhatsApp.
*had nothing to do with the way I invited them, most do the invite only not even a poll. I only had to do that because hardly anyone responded to the invite!
Most people don’t do a poll because that’s weird. A low response to what you think is a clear invitation suggests you might need to follow up and be more specific. Again, we don’t now if the poll was worded “respond here whether you will be attending the party” or “can you attend?” But something was wonky because people responded but didn’t show up, and a whole load of others didn’t respond to OP but did to an invite the following day.
Occam’s Razor: the most likely reason is that OP’s communications were unclear (as are her posts on here). It’s far less likely that an entire group decided to actively upset OP and her small child for shits and giggles. We will never know though as OP isn’t here to enlighten us.