Maintenance for the Children is more of a CMS procedure rather than the Courts. Best to apply to the CMS as soon as you can. It will cost 20 pounds, but it is worth it as it is binding. Before you call them have to hand information about husband such as; full name, date of birth, address, place of work, name of employer, earnings if known and ideally his National Insurance number.
There is an online calculator that can be used for Child Maintenance. Divide your Husband's annual earnings by 365 then multiply by 7 to get the gross weekly amount. Other details to enter are the number of nights children will stay with their father. If more than 52 nights per year (average one night per week) the Child Maintenance will be reduced.
If you are applying for Spousal Maintenance then you will need to prepare a budget for all essential needs such as; housing, council tax, utilities, food, clothing, etc. Add it all up and then subtract your own income. The difference will be the Spousal Maintenance you apply for.
Sounds simple, but in reality Spousal Maintenance is a complicated subject as unlike Child Maintenance there is no defined formula. Courts will take many factors into account when deciding whether or not Spousal Maintenance is applicable.
If after your husband has paid for his own needs and the child maintenance he has little or no disposable income Court are likely not to award Spousal Maintenance as plunging one partner into difficulty/hardship for the benefit of the other would be considered unfair.
If Spousal Maintenance is awarded it may only be till the youngest child reaches 7 as there was a ruling in 2015 that once children are aged 7 and over it is possible for the parent with care to find a part time job.
If you are struggling at the moment ask your solicitor about a MPS (Maintenance Pending Suit). This is a Court procedure that enables the Courts to make an interim order for maintenance to tide people over until the Financial Settlement has been agreed or ordered by the Courts.
Hope you can settle amicably as if one or both partners turn the Divorce into a contest the Legal costs can spiral rapidly and there will less at the end to divide between the two partners.
Good luck.