I work in an area where families usually have 4 children+ Almost all the families claim child benefit, FSM, council’s EMA and additional school holidays money top ups, adult free dentistry, prescriptions as the declared family income is &16k or less.
However, most of the dads also work cash in hand in restaurants and as Uber drivers to supplement the family income. If you have 4+ children you would have to earn at least 100k in order to have a MC lifestyle i.e house in a reasonable area , bedroom for each dc, a couple of holidays a year, activities for dcs, big enough car. If you were on £30k a year you will have to be reliant on various benefits to do this