Definitely not a silly question!! Its seems confusing b/c the foods we associate with fiber are, well, fiberous. Fibers are not destoyed as the "fibers" are microscopic. The molecule cellulose if the one that keeps things "regular" and although I imagine there are machines that could break it up, I'm sure you do not have one in your home

Actually you can get fiber suppliments that have no texture whatsoever, not sure about the UK but in the states the best one is Benefiber. I actually put it in tons of my 3 yr old's food ie. mac-n-cheese, pancakes, oatmeal, b/c he doesn't eat his veggies v. well. He can't taste the difference.
PS, make sure that as you add fiber and fiber suppliments that your little one is getting plenty of fluids as well. If you are on formula you may want to talk to you dr. about adding some watered down juices to help your lo, also ask about whether fiber suppliments would be appropriate for your baby.
Hope this helps!