For product photography and toddlers, I'd opt for an external flash before a new lens. For kids, it will freeze the motion better. For product photography, you can setup some really cheap light boxes to get nice even lighting. If you're set on buying a lens for those, I'd recommend any of the 24-70'ish f/2.8 lenses or even a nice 50mm f/1.4 prime. But frankly, flash is the way to go there.
As far as travel lenses go - it just depends on what you want to shoot travel wise. Some people want one ultra zoom lenses to cover everything but compromise on quality. Some people take a series of lenses and deal with the 'hassle' of changing lenses to optimize quality. Rather than rehash all that - take a look here.