I think it depends on what your primary goal is.
Do you want people to get the ice cream, sit down, eat and leave? If yes. Then just add the extra seating. Maybe put a stand in there for cheap, for you, topping people can add on their own at no cost. I'm sure kids would love it. Like Hershey's syrup, crushed walnuts, those fake candy crushed walnuts and sprinkles.
One option is a simple food option. You don't want to waste a bunch of space. Plus keep it simple. Like hot dogs. Caspers hot dogs was always busy in California. Sell steamed hot dogs, chili dogs and chips. Really good and big hot dogs aren't that hard to do. Keep the menu really simple to speed prep and reduce space usage. Just think how small hot dog carts are. You'd just be going a step above. Do just those three items and the normal condiments (ketchup, mustard, relish, onion). This also makes the prospect more attractive to parents. As they can stop at one place for them and their kids to eat and get a treat. Rather than two stops.
If you want something more ice cream related. Add more seating and a real soda jerk. That's pretty novel. Getting soda the old fashioned way and seeing a soda jerk ply their trade. Perhaps do one side of the shop soda jerk and ice cream. The other room all seating. That way people sitting aren't crowded by people in line and going to the bathroom.
Speaking of bathrooms. This is a Covid moving, hopefully, to post covid world. Touchless entry/exit both for the shop and bathroom is a plus. Also touchless flush, handwashing, soap and drying in the bathrooms. If you want to reduce the mess. Put those fake fly stickers in the urinals and toilets. Maybe separate small bathrooms and avoid the gendered bathroom kerfuffle. Even before covid. I always hated having to touch the doors of businesses. Knowing how bad people are about washing their hands. Bathrooms are the worst.
A bonus with side dining room only. You can put touch screen ordering stations on the tables. That way people who don't want to wait in line may sit down and order. I know one thing I always hated in ice cream shops. Was standing in line while people hem and haw over their order.
For dine in. Offer glassware and metal utensils. For take out. Use biodegradable containers, straws and utensils. That'll give you eco points for more conscientious people using the shop. While the glass bowls will add a touch of flare for the nostalgia factor of a real ice cream parlor. For dine in customers. Plus you could sell stuff like a really well made ice cream scoop, branded glasses and swirly straws. Basically making your shop a bit higher end (higher price). You want to stand out not try to compete directly with Baskin Robbins. You also don't want to be the cheapest because then you are a commodity and someone else is willing to sell cheaper.
Really unless you add something which keeps people spending. You're going to have your valuable 40 seats (10 tables) being used up. While the kids screw around in the play room.
If you want something to keep people there longer but have more room. Maybe some more tables. Then use arcade machines. Maybe a whack a mole. I thought arcade tables. Then realized arcade tables plus kids and ice cream. Equals horribly sticky buttons. I'm not sure if those classic arcades can be modified for cards. So, maybe tokens and charge 50¢ or $1 per token. Rather than having people dump a ton of tokens in the machines. The days of 25¢ arcades are long gone.
As for a ball pit. Little kids pee in ball pits. That's not the worst thing they do in there. Do you or does your partner want to deal with that? If that doesn't turn you off. Ball pits are for little children. Not only does it add nothing for older children or adults. Being seen as a place for little kids can make older children and teens adverse to going there. Plus people are only going to buy ice cream then the adults will sit around taking up seating while their kid plays.
Of course this all really depends on where you are located. I'm thinking of a store in a shopping center with a Whole Foods, Publix or Trader Joes. Not one next to a Walmart, gas station or Dollar store. Worse yet, no big foot traffic driver.
At any rate. Good luck. Restaurants are tough. Now is either one of the worst times or best times to start one. Really dependent on if businesses can keep opening up and customers are willing to return to restaurants. Given how many restaurants failed last year. There's a lot of vacancies for eateries now.
