I don't have grands yet, and my girls are way beyond this stage, but I've seen moms struggling with their active little ones and getting frustrated not being able to concentrate on fabric/whatever selections and leave in a
hurry without being able to take the time to shop.
How about a small "contained" fun place for the little ones to play in while Mom/Grandma shop? Maybe a tv/dvd player, large legos, books, pegs - age appropriate interesting stuff
they MAY not have at home to play with. You wouldn't have to hire full time staff to oversee as it would be sporatic, but rotate your regular staff to be the "eyes on the kiddos" when needed.
Coffee/water are great ideas. Shopping is thirsty work! A nice piece of chocolate with the store logo/name on the wrapper would be fun! If people are able (after buying so much), I see nothing wrong with a donation-type jar. Maybe
have a donation jar drawing monthly to win a small prize (pin cushion, transfer pencil, etc.)Make a small donation, take a chance to win a small prize.
Maybe after you're up and running, offer once-monthly free class. Our LQS does this, and it has rewards for all. People get to learn or hone-up on a skill, get a 10% discount coupon for that day only, and the cash register stays BUSY. Fun and worth it for all.
Everyone has great ideas for your shop along with the ones you've probably already come up with. Good luck on your new
endeavor and I wish you much success!