Its a how long is a piece of string question and depends in part on the age of the child and the lifestyle you want to maintain.
My son was nearly 8 so was immediately costing a small fortune in shoes, but was at school so I had no childcare costs when I went back to work.
Some people are very good at shopping in charity shops, collecting vouchers, points, maximising discounts, take picnics everywhere etc. Some people want to dress their kids in designer gear. I’m somewhere inbetween - Next and Fat face served us well, if I can get stuff in sales I will but don’t go out of my way. I did spend a lot in coffee shops as I’m a single adopter and it was just nice to be in the same place as other adults at times.
Work out a budget, food, clothes, entertainment/activities etc. Assuming that life may have returned to some level of normality by the time you are placed, musuems, galleries, libraries often have free, or very cheap childrens activities.
Consider things like National trust or English Heritage memberships - always good for cheap days out.
One thing I did which came in very handy was to stock up on about three months worth of non perishable groceries which reduced my shopping bill for those last months without pay. I also made sure I was well kitted out with good shoes, coat, ‘mum’ clothes whilst I still had a full salary. I don’t think I bought clothes for me for about 18 months after he came home.
