It would've been helpful if the OP said where she was. I strongly suspect Australia, in which case this advice isn't necessarily the best, based on how our childcare subsidy works.
Basically, the government subsidies a percentage of your hourly costs (the percentage is applied to the first $12.20 per hour - anything above that is 100% paid by you). Your percentage is based on your income and other factors. Second and subsequent children get an extra 30% subsidy, up to a maximum of 95%.
So if the OP would be paying 95% for a second child, then she'd be paying somewhere between 60 and 85% (which I think is the upper % limit for first children).
But this only goes until the first child's 6th birthday, so if her older kid is 6, then the second child won't benefit from the additional subsidy.
A smaller age gap will mean a few tighter years, but over the early childhood years, they will have paid a lot less for the second child (ie the value of the additional 30% discount, 5 days per week, at $122 per day is about $9k AUD per year). For a lot of families, this is worthwhile (hence the policy decision...)