Child care is one of the costs of having children. There are other costs.
I tend to agree that the UCCB is not going to cover the cost of child care for even one kid. It's not enough, but it's a benefit. It helps.
Quebec has gone a totally different way, whereby child care is almost totally subsidized by taxpayers, and that has led to some economic benefits. I don't think it's self-financing, but the evidence is there.
Quebec also started at the low point, when mothers had one of the lowest participation rates in the country, so Quebec had some catching up to do.
Now, if you're asking me whether the UCCB is a support to families with children, obviously it is.