Some people have been complaining that the​ children's playground at a municipal park is too small and is in need of repair

Note that:

Voluntary response bias occurs when individuals can choose on their own whether to participate in the sample.

Undercoverage occurs when the sampling scheme biases the sample in such a way that part of the population has less representation in the sample than it does in the population as a whole.

Response bias is anything in the survey design that influences responses towards a particular response.

For the case above, 

The sampling scheme suffers from voluntary response bias. Only parents who choose to visit the park and feel strongly about the issue are likely to respond.

The sampling scheme suffers from​ undercoverage, because only people who come to the park to use the playground will respond. Parents who are dissatisfied with the playground will not come.