If there is no outside I don't think you can say there is an inside, dosn't confused the concepts of solid and hollow objects for the kids? Maybe better to consider the universe as an empty solid, so we are the "part" of the universe, not inside or outside. maybe a jar of water and teaspoon of oil could be used to demonstrate the empty space is like the water in the jar (universe) and stars and planets the balls of oil. Ah says little Johnnie "but the jar has and outside" so you imagine a swimming pool and a bucket of oil, and when he talks about tiles ask him if he's been to the beach
It is a tricky concept and there are logic problems everywhere. Maybe we need magic where we can summon a small ball full of dots and you move your hands apart and the ball grows.
Observable universe = 48 BLY? Age = 14 BLY? Shouldnt this be around the other way, that would explain difficulties explaining.
I thought around 14 BLY is as far as we've observed so in that time (14billion years) the region will have expanded out to about 48 BLY in size.
Space is Big, Really really big, You may think its a long way down the road to the chemist but thats peanuts compared to space.
I'm happy with Douglas Adams' explanation