I’d have a carriage for all the miserable folk who love morning about other people’s kids. Let them inflict their entitled opinions on each other.
This is public transport, it comes with the territory that there could be a family of four sat on a table on the opposite side of the aisle. If you value your own personal environment that highly, get in the car. In my experience, most kids are well behaved and just like adults, a few get out of hand and it is fair to say that noisy adults are far more annoying than noisy kids.
A crying baby, tired or hyper children, an adult talking loudly on a phone, an adult streaming music or a film loudly, hen and stag parties - all can be frustrating. Yet the number of times young children break everyone’s peace and quiet is far more rare than the adults.