I've only skim read so forgive me if this has already been suggested but I found the most helpful learning tool for numeracy facts teaching to a gifted child was to explain the system. We use the decimal number system and so I explained what that meant. I demonstrated how it differed from other number systems (ones they were familiar with like roman numerals and others unfamiliar to them) but essential explained the system, ensured it was logical and there was nothing weird or complicated about it. The best visual tools for this are the base ten blocks (which come in handy for decimals and much more later on too)