Northamptonshire county council is facing a series of legal challenges over plans to close 21 libraries, after a young resident applied for a judicial review of a decision campaigners say will have a “devastating impact” on families.

The action joins a separate case launched by residents in support of local libraries, as well as a formal complaint submitted to the secretary of state for culture, Matt Hancock, by the libraries body Cilip, which suggests the council has failed to meet its statutory duty to provide a “comprehensive and efficient” library service. The closures, which councillors approved in February, have been branded “monstrous” by the Northampton comics author Alan Moore.

Law firm Irwin Mitchell said on Thursday that it had issued an application for a judicial review and an urgent hearing after being instructed to act for a child and their family.

“Many people using the library services are children, or are elderly, disabled, or from low-income households, and they may struggle to access the library provision in larger towns,” said Irwin Mitchell’s Caroline Barrett. “These cuts are extensive and our client is concerned that this will have a very significant impact upon their ability to access a library service and the impact on local residents, many of whom live in rural areas. Our clients believe that, if implemented, these cuts will have a huge detrimental impact on the local community in Northamptonshire.”

Barrett said her client believes the council “failed to carry out a lawful public consultation into the proposals and has not conducted a full and lawful assessment of how vulnerable people will be affected”, has also “not considered how to promote and safeguard the welfare of local children”, and is failing to provide the statutory requirement of a comprehensive public library service.

The child’s mother said: “These cuts are not fair. They will have a devastating impact on families like ourselves, but also on the most vulnerable people within our community. The libraries offer us so much more than just books. They offer residents access to the relevant district council’s one-stop shop, blue badge and bus pass renewal, children’s services and plenty more services that residents rely on.”

The law firm Watkins and Gunn, which is representing local campaign groups in the second legal challenge, has also applied for a judicial review. Watkins and Gunn’s Michael Imperato said there were “several holes” in the council’s decision.

Hancock is currently considering whether to launch a government inquiry into the situation in Northamptonshire, which declared itself effectively bankrupt earlier this year. The closures would leave Northamptonshire with eight large and seven medium branches – one library for every 60,000 residents, according to the all-party parliamentary group for libraries.