My idea is that companies should be required to provide subsidised onsite childcare.
In the office of the future, onsite childcare should be seen as a standard provision that companies make, similar to having serviced kitchen areas, first aid rooms or receptions. It needs to be run as not for profit, ideally with tax deductions for the company. Staff choosing to use the service should pay a nominal fee to contribute to costs, which can also be salary sacrificed. Being able to bring your child to the office has the added benefit of no drop-offs / pick-ups (more time and cost savings) and would encourage women, and particularly single parents, to stay in the workplace thanks to the convenience and affordability.
For companies operating from large office buildings in a city precinct, it might be more efficient that the building itself is required to offer a child care service (again, not for profit) which the tenant businesses can subsidise for their employees making use of it. This pooled resource may provide some economy of scale and help to reduce cost for individual companies, and especially for the smaller ones with fewer staff or restrictive budgets.
Final thought on costs is why are they high to start with? Childcare is a highly regulated industry with high audit and governance overheads. In an environment where parents are able to play a closer role in the childcare service, some of this overhead may benefit from industry review.