You are nowhere near me but I have some advice as I frequent soft play user with a choice of 10 near me, wining factors as follows:
Vegetables with kids meals eg carrot sticks, peas, sweetcorn.
Homemade kids meals - very easy to offer cottage pie, hidden vegetable tomato sauce with pasta and cheese. Homemade pizza muffins, etc
Fruit available - best one offers a small bowl of fruit (eg strawberries and grapes for £1)
Drinks - look into this, whilst lots of people have no problem giving any drink, I do. Offer fresh apple juice/orange juice carton and small bottles of water. Sugar free options often contain nasties that we try to avoid.
If you have space it's nice to run a little activity session throughout the day, paper and pens, play-do, story book corner or sing/dance time - keep it simple but a very effective way if getting all the kids to be calm for a few mins and allow their parents to prepare them for going home.
Don't have baby toys, they will be gnawed on and become grubby very quickly. I avoid places with these. Small ride on or walker equipment is great.
A section for teeny babies, sensory with fibre optics or similar is a real winner.
Distinct under 4 zone for toddlers who need to be watched by mothers with babies too.
Don't make it too hard for parents to see into or get into the main frame. A soft play near me has a section in the ceiling where you can't see the kids. I avoid this.
Special offer on after school entry to include a meal, snack or drink.
Am sure you've had lots of these ideas but they are problems for me so thought i'd mention. HTH 