>Should I get a voucher if I pack my kids lunch?

Yes. And no. The gov gives the child X$ per week/month/year. The child parents use that money to take care of the child.

Society benefit from children that are well taken care of. Mechanisms to ensure that they are well taken care of are needed. Well funded daycare centers are one of the mechanism. A well funded household with a parent/grand parent/uncle is another one. In both case, an agency is in place to ensure the wellness level of the child.