We've attended both munches & very informal get togethers.
Generally if they are held in a public place like park or restaurant the newbies will feel less threatened because they are familiar with what they are seeing.
The one restaurant our Brunches used to be held in had a back room where we could all go, talk up a storm, meet new people & not worry about the general public hearing things which might upset them or things which the kids ought not to hear. That back room would hold 30 or so people and the wait staff were very courteous and attentive without standing at your elbow.
Another venue had a back room as well, not as big, but was quite adequate for our needs.
Both of these were family restaurants & on main line bus routes so those without reliable transportation could get there as well.
We've had them in parks and pubs (we're a double university town plus multiple colleges). For those of us who are financially challenged the park is a wonderful idea--there are many different things to do, couples/diads/etc. can go off by themselves for a few minutes, they are kid friendly if you can't find a babysitter.
Check the local poly calendar for a night when there's little to nothing happening & set the date by that (you might want to check the local BDSM calendar as well since they two lifestyles do tend to go well together), check with the venue you choose to use whether that day & time are free & book it if it is. You will also want to make sure that they know everyone gets their own bill so you, as host, don't get stuck with it.
Our local BDSM community simply bills itself as an internet group so when newbies get there they just have to ask for the internet group & they'll be directed to us.
If you choose an outdoor venue you will also want to consider the long term weather forecast, lol, and maybe have an alternate venue available just in case.
When we meet at the park it's a pot luck, kids and furbabies are welcome.