No, no, no !!
Naked Twister is much better
I second croquet, and suggest Poop the Pear. It’s a team relay game my mom taught me.
Divide into teams. I’d suggest 3-6 people per team, 2-4 teams – sort it out depending upon how many want to play. The teams line up behind a start line; the goal (one per team) is a receptacle about 15-20’ away (adjust as seems right). The receptacles can be grocery bags or desk-size trash cans. Each team needs a “pear” – I’ve never done it with an actual pear, though we have used apples, oranges, and softballs. Tennis balls could work.
The first member of each team stuffs the “pear” into his crotch and then waddles towards the goal. If the pear falls out, he must stop and reinsert it. Upon reaching the goal, he positions his crotch over the top and drops the pear into it. The pear must be “pooped” into the goal. Having done that, he grabs the pear, runs back to the start line, and hands it to his next team member, who proceeds to insert, waddle, and poop, etc. The game is won by the team whose final pooper hits the goal first. It’s fun to try, and a hoot to watch.
Rent a hot tub and get a keg. Guaranteed good times for young adults 
Or water balloons. Although if you want to avoid loathing yourself the next day for coming up with such a stupid idea, after the balloons are all gone, offer a prize for whoever can pick up the most itty-bitty pieces of colorful latex that will be scattered all over the place.
Is there another way to play it 
Often best with some sort of slipper substance applied.
We really like Catchphrase at things like this. It’s flexible and easy to do, and fun either to play or kibbitz. You can have an almost unlimited number of people playing. My almost-twenty daughter suggested having a couple decks of cards out, because there’s a bunch of games right there, and people can pick them up at will.
I like the idea of just having things around for people to play or not, and usually the groups will shift and change as the day goes on.
And yeah, Apples to Apples is a great idea.
Drinking and cards.
Euchre is a great way to kill an evening and braincells.
We usually bring out the Bocce set for our backyard bashes. Tends to be a big hit. Easy to learn, and you don’t need a regulation court or anything to have fun. We just play on the backyard as is.
And of course some good tunes can’t hurt.
Howabout naked Cornhole?
I would discourage board games at a BBQ/picnic. Either they require just a handful of people - which decreases the number of people interacting with each other; or they require a large number of people - which forces people into a group activity. Keep them outside! Bocce ball and cornhole are great, and keep people with the larger group as well.
A friend set up a balloon pop at his last party, and had “tasks” or “prizes” for people inside the balloons. It was more of an alcohol-centric party, so the tasks were things like “get a kiss from someone”, “tell a secret to _____” or “finish your beverage”. But the prizes were fun as well - “assign 5 drinks to anyone”, “force a secret from someone”, etc.
What’s the setup? Big backyard? Park?
Your friends are in their late teens and early 20s and have young kids already?
For the type of party you described here are some of my suggestions:
-Since you are having a piñata, maybe go with a Mexican fiesta theme. Dos Equis and Corona beer, margaritas, tacos, nachos, etc.
-Bored games suck
-Go with wiffleball baseball, horseshoes, bocce, badmitten and basketball (if you have a hoop in your driveway). Probably avoid Jarts.
-Since your friends do drink and are not, in fact, 45 years old, I would reserve a table for playing Quarters / Asshole / Beruit or whatever drinking games you are in to.
-Since your tastes in music can’t be trusted, I would go with either leaving on a Top 40 station or making a playlist with the following guidelines:
- Keep it mostly to radio-friendly tunes from the past 2-3 years
- Throw in a handful of nostalgia tunes everyone loves from 10-20 years ago
- Keep things mellow-ish, avoid most metal, heavy rap or crazy-ass dance music
- Artists like Bob Marley or Jimmy Buffet are allways outdoor barbeque favorites
My brother lives in Ohio and has mentioned it repeatedly. I think it is an Ohio thing.
We play it here in Maryland, too.
Two words: Rock Band
One thing I do recommend is pick people who will enjoy playing. Nothing worse than going to a party with games and finding a bunch of Negative Nellies who complain about games and refuse to play any of them.
OK you would need a generator. Didnt see the picnic part. I suck, carry on.
I see a lot of “yuppies” having these outdoor dinners and they seem to play a lot of horseshoes or darts or other throwing type games.
I second this, and may I refer you to http://www.dinnerandamurder.com/?
I did The Immortal Murders for SWMBO’s 50th birthday. We had a total blast with it.
There’s also nothing worse than being forced to divide up into teams and play silly games you don’t enjoy, when all you were expecting was a casual picnic with good food and conversation. That’s why the OP needs to either make the games optional, or else make it clear on the invitation that the focus of the party is games and everyone should expect to play.
I love games and so does my family, so our events tend to be centered around them. New games are always fun, but the ones we go back to over and over are Apples to Apples and Loaded Questions. Apples to Apples is better with newer people and bigger groups, so we usually play that first, and then Loaded Questions (which is, appropriately, far more fun when everyone is loaded). Both are games that value a bit of creativity and wit, and they’re both easily locatable at fine stores like Target.
We also like to bring out the Nintendo Wii and play the easiest, most group-friendly games we have – e.g. Wii Sports, Boom Blox, Wii Play, etc. Most people can be arm-twisted into at least trying it, and those that can’t can at least watch and enjoy the hilarity of people fumbling around.
Any kind of game can be fun with the right crowd. We’ve done a lot of bachelorettes lately and games are a nice icebreaker while people are first there and getting bored with small talk.
I like the murder mystery party idea, I may have to try that one!
How about a swingers party? 