It is better to treat these as separate issues. Some people need additional assistance from the state as they age. We should decide how much support we'd like to provide, and provide it without bias.

We might also want to encourage some level of additional population growth. This is best done by providing support for parents.

It is better to incentivize behavior by providing services that help people do the things we want. Attempting to punish people will just cause anger, and even if the punishment is doled out for good reason (which, I'd say it isn't a good reason in this case), some level of misstargeting is inevitable.