In France they have a nice formula where you count children as people you share with, and the single-income family could use that.
In the United States they have head of household. You can be a single parent and you can share with your children. So a single parent can benefit from that.
The other thing I think, if we talk about the current system, is that it's very imbalanced. The wealthy end up wealthy. Basically, if we're talking about adjusting it, it may be that the adjustment will be unequal in order to get an equality. I don't think we should look at the inequality of the adjustment as a problem.
I mean, if low-income people get anything, it's better than what they have. Income splitting would help day care workers who are low paid.