you can slowly talk to your partner about how to design a good future together and start a frugal life, it won't take long to make this movement a habit, the goal is to achieve financial freedom, the sooner the better.
for children's school fees, you can include that in the list, you can set aside the income you have for your education costs until they all graduate from school (sorry, not financial advice, I am starting this movement)
Op is a good suggestion but those are easier said than done because a partner whom there monthly salary is not enough for them will hardly think about that and not that they are not concerned about the future of there children but the stability is the problem because is always here and then to eat up a lot of money you have saved, when you have children unless you have a very high paid job will you be able to spend and keep for the future because children are very selective to almost everything, considering how costly things can be, so is a big deal, but to break through from being too dried up on this kind of situation is when you have already started the preparation before then such as a source that no matter how little the profit is it can feed your family so that your salary will not be tide up for immediate consumption anymore.