Kinda comes across as a group of lazy parents expecting you to do even the fun stuff with their kids. If they want their kids at cosmic adventure they can take them.
With the loss of JK kids the age mix for sure has gotten younger and it is no longer a case of letting a baby tag along with the bigger group - there are no bigger ones any more.
Also with the ELECT concept what about using that to persuade them that a change of focus is needed away from things you plan to things you facilitate so you will be setting up the play space for their learning and doing less outings as a result.
Also never absorb any of the costs - make them cough up the total amount of money.
What happens if you simply stop all outings and when they whine just tell them to take their kids there themselves on their own time and then leave it at that. Would they leave in a huff but come back the next day even if their nose is out of joint for awhile or would they actually leave and never come back?
I am clear right up front we do not do outings and parents choose me because of that and the others move on to someone else.