although I have never done it, I don't see any reason why you couldn't order and get a "virgin" lapu lapu. Alternatively, you could just ask for whatever drink you want served in a pineapple. I'm sure if you flashed a big tip in their face, and they weren't too busy, you could do it. I think you may have to pay dearly for it though, the cost difference between a mai tai and a lapu (basically same drink served in a pineapple) is about $5. The bartender may have difficulty deciding on a price for you. As long as you are willing to pay the same price as a regular lapu lapu, I would think you could do this.
Oh, just thought: you could order the lapu lapu for an adult, then pour it into a plastic cup (the bartender could give you one) and then fill the pineapple with a drink that your child will drink. Don't worry, the pineapple won't taste like alcohol if you do this right away as it is served.
One tip: you can save the pineapple in your room fridge and use it again the next day.