As an employer, a parent, and someone watching my own children and inlaws navigate parenthood, let me say this really clearly:
If someone (such as your boss) thinks "work/life balance" means letting parents do less work and making non-parents make up for it, then that someone is doing it wrong.
Work/life balance means that everyone has a life outside work, and employers respect and celebrate that. They don't count on being able to get overtime from people on no notice, on people answering emails at midnight, on cancelling and postponing vacations. For anyone.
I suppose if, once in a while, some emergency overtime is needed, management might turn to those without family obligations (which is more than kids: there was a time I had elders to care for, and another time when my spouse had to set work aside to care for me while I was dying (I got better, we live in the future), and so on) and ask them to do that, and then reward them in some way - an extra day off, or some money - when they do. But not regularly, and not "you have to do it because you don't have family obligations." More like:
We're really stuck here. Because of [bad planning, bad luck, a decision to try to accommodate an unreasonable request from a client] we need someone to X. Nobody will be forced to X. If nobody does, [consequence to company such as losing the contract or incurring a financial penalty.] Anyone who does will get [reward]. Can we make this work?
This is way harder than "let's give the parents a break." It requires a true commitment to the entirety of the lives people live outside the office. It requires honesty about the reasons things are asked of staff. It also requires a willingness to take the consequences of things that happen if staff is not willing to bail management out at the expense of their personal lives.
Now, how should you raise this to management? Ask for some quiet time with your manager and explain that "life" is more than just raising children. It's caring for parents, leading a volunteer organization, caring for a spouse, having a hobby, working out, self-care of all kinds. Ask if, in future, the "life" choices of all employees, not just parents, be considered. Tell your boss how much you would appreciate that. If you can, say how you felt when you were "voluntold" because you are not a parent. Try not to describe specifically what your nonparenting life needs are. It shouldn't matter. You can also mention that offering rewards means that people will offer to do it rather than having to be told that they must because they don't have children.