I don't think it's too far in advance at all. Surely if you currently have no plans for anything important in the first week in June, the chances are high that nothing important will come up. If you had a holiday planned or a wedding to go to, or a 40th birthday party in a hall with a buffet and disco or something, this kind of thing would have been arranged a long time ago.
What on earth could come up now, just 11-12 weeks before the 8th of June? Just rsvp 'yes' and put it in your diary or online calendar. I really cannot see the problem. How on earth do you cope when you go to the dentist, and they ask you to book your next appointment for 6 months time? and other stuff like that... ?
I would much rather have 3 months notice than just a week or 2. If it was very short notice, the chances are high that I would already have plans.
Re, this...
"I work weekends some weekends so when it’s far ahead I can’t commit to more than 6 weeks ahead."
in which case a quick message to the parents - sorry I'm not sure if I'm working that weekend, I'll get back to you when I get my rota on x date - is surely fine? It's really not that big a deal.
This. ^ If you are someone who only gets a rota one month to six weeks in advance, then just tell them you hope to come, but will tell them for sure, in early May, as you don't get your shifts for June til then.