I didn't see any medical (co pays, prescriptions, dentist, eye doc, eye glasses, etc).
Also missing clothes, kid expenses (both school and non-school related), vacation, gifts, charity. Other than that it seems like a pretty good budget.
I was gonna comment on this, yeah. Gifts, especially, when you have a kid... both of the 'oh crap you got invited to this birthday party' variety (if it helps, I keep a box of bought-on-sale art supplies and the like, things that are gender-neutral and can be put together in a nice useful non-clutter-y gift basket for basically any kid between ages 4 and 10, for not more than 10$/party) and of the 'Christmas and birthdays happen every year and are not a surprise, you should plan for these' variety.
Vacation: are you taking it? Who is paying (or providing) childcare when school is closed? Is this in your divorce agreement.
Clothes: for the kid, that should be in your divorce agreement (check how it's worded - you don't wanna be paying for 50% of designer jeans because your ex wants them for the kid) but clothing wears out and needs replacing. Also winter boots and snowsuits are expensive and get grown out of every year or two, kids will unexpectedly lose one sneaker (HOW???), etc. If you like thrifting, that's a minimal budget, but if, like me, you're in a place with minimal thift stores (or stupidly priced ones), then check out, say, Old Navy online (it's the best I've found in terms of new clothing quality vs price) and see what a wardrobe would cost for a season, and split it out by month. (Also learn how to patch/darn things, it saves the clothing budget, no joke)
Also: life insurance? Are you required to have any in your divorce settlement? Do you WANT to have a small policy, to care for your kid if something happens to you? Renter's insurance - depending on your ability to set yourself back on your feet in case of, say, a fire and total loss of all your posessions, might be worth 20-30$/month (especially if you work from home and your earning ability relies on expensive computers).
Looking at my family budget, other things that I see as absent in ours: restaurant (not that you necessarily eat out much, but a pint out with friends once a month adds up. Not a lot, but it exists. Unless you loop that into your grocery budget - basically make sure you plan for money to cover your ACTUAL expenses, not just your planned looks-good-on-paper expenses). Medical co-pays? I mean, we're in a place where we get public system coverage for EVERYTHING, basically, but we still count 20$/month for general 'health' spending (cream for that rash, a new bottle of advil, a bit towards glasses replacement, cough syrup when needed, prescription if needed, etc - it adds up). If you're in the US, you're likely to need more. What's your monthly average of health-related spending over the past 2 years, say?
Finally - how do you count your household goods? Cleaning supplies, ziplocks, replacement sheets when yours get threadbare, picture frames or random decor if you care about that, furniture, appliance repair/replacement, etc - again, it adds up. And what about unexpected things? Like, oops, our sheets just ripped, and we need new ones NOW? Or the fridge just broke, repairs are $$? We put 100$/month into a YNAB 'unexpected spending and house set-up' category, though we have a large house that we just built and so the set-up needed was considerable. We typically spend 20-30$ on decor/furniture/paint (yay Craigslist and carpentry skills...) and the rest goes into a 'when the fridge breaks' fund. Depending on what you care about a what you're responsible for (aka: if the fridge is your landlord's problem) you might need more or less.
Do you have any decent view on what your family has actually spent over the past 2 years? Sure, some of that is your Ex or is housing-related, but going through it and making sure that you've got a good idea of what your lifestyle actually entails might be a good starting point. You don't wanna hit summer and be like "shit! summer camp! 500$!" for example. You wanna know what you usually pay NOW so that you can eitehr budget that 500$ OR set expectations that it ain't happening this year.
