I just really don't know how. 
There's DH (eats a lot, is 6'4"), me (trying to stick with mostly veg and protein as I feel best this way. I have celiac disease and so gluten is out; also I react strongly to sugar, even very sugary fruits, so try not to eat too much of that even though I love it ), DS who is seven, and DD who is 16 months.
Additionally, I childmind three days a week, so on Tuesdays and Thursdays I have an additional five year old, four year old, and 15 month old, and on Wednesdays I also have the four year old and 15 month old. When I childmind I provide lunch and snack. I also like to do a baking/cooking project on Tuesdays with the older mindees.
DH usually takes leftovers from dinner for his lunch the next day. DS takes a packed lunch about 50% of the time and buys school lunch the rest of the time. School lunch costs $2.05. When it gets too cold for me to walk him to school he will go early (so DH can drop him off before work) and eat breakfast at a cost of $1.10. (We're American and Google isn't working for me to do dollars to pounds for some reason
)
So. I really need to meal plan and have a budget because it seems like we are always running off to the store for something or running out of something, or all of a sudden there's nothing to eat.
Any ideas? I know this is a lot of information!
No one is very picky; besides my gluten/sugar issues everyone will pretty much eat everything. I've just learned to make French bread and a few times a week we can have that for dinner with a big pot of soup and some fruit, which seems cheap and filling.
I like to stay away from anything too processed. There is an organic farm down the road which I would love to get more of our meat, etc from if I can make room in the budget. My FIL usually gives us eggs but a lot of his chickens have just been killed by a neighbor dog :(, but at some point eggs will be free.
Our local grocery store is a bit expensive but we do get to Aldi (about 45 minutes away) every few weeks.
So...where should I start? :)