More than 10,000 parents of US citizens are likely to be detained in California by immigration authorities every year.
That's according to Human Rights Watch, which is calling on California to ensure those detained are kept in dignified conditions and have access to lawyers.
A report created by Human Rights Watch on the matter used data from federal immigration authorities, after it made a freedom of information request.
It analysed data from a four and a half year period, covering almost 300,000 detentions of migrants in California to create the figures about immigrants.
Not all of the data showed how many immigrants had children, but one nine-month period did and the group have used this to estimate that about 42% of those detained have children who are citizens in the US.
Researcher Clara Long said: “With 15% of all US immigration detainees held in California, state legislation aimed at enforcing humane detention standards and addressing fundamental due process failures is crucial.”
Human Rights Watch already believes standards in the detention system are inhumane and this, combined with poor medical care, has led to unnecessary deaths.
It also believes the Trump administration's decision to fast-track deportation measures now means migrants struggle to have a fair hearing.
Long said: “State leaders should address due process gaps for everyone in immigration detention, no matter their situation or history.”
The Californian assembly is currently considering revising the budget for legal representation for detained immigrants.
Senate Bill 29 is also being considered by California state legislature. If passed, it would mean detention centres had to meet specific civil detention standards for immigrants.
This would include privacy, medical care, legal services and not allowing harassment or involuntary segregation.