You wait til he/she gets older, it gets much harder! I regularly walk up to a couple of miles with a 3 year old on my shoulders, and occasionally have a 6 year old up there for half a mile or so (just to diffuse carrying jealousy). Sometimes I can almost feel my spine compressing as I walk, and have to peel my collar off my skin when I get home. Still, 6 years of carrying kids about have left me fitter than I might have been otherwise! :)