The basic question here isn't, "Which lens?"
It is, "Who knows better than anyone else which lens will work for the intended usage?"
I think the retired professional photographer with 31 years experience can probably best answer this question. More than anyone else he will know what he needs to do what he wants with his new camera.

So then the next question is, "Which is more important to me? Potentially spending $500-1000 on the wrong lens so that I can get the satisfaction of 'surprising' my Dad with a gift or talking to him ahead of time and getting his thoughts on the matter?"
Only you can answer that question.

There may be some middle ground. Buy from a reputable source such as amazon.com, B&H, or Adorama that allows for full returns of unused items for up to 30 days after purchase. Then you can have a little of both: You get to surprise him but you also have the option of getting his input and swapping the lens out if necessary. Be aware that if you buy a "kit" or "bundle" you will need to return the camera as well as the lens to exchange them both, even if you want the same model body.

As far as which single lens is best for both family photos and sports: There isn't one. You need a good general purpose lens in the normal focal length range for family photos. You need the fastest (widest maximum aperture) telephoto lens you can afford for sports. Here's a good run-down of general purpose lenses for Canon APS-C cameras and telephoto lenses for Canon cameras.

If my budget were so limited that after purchasing a 70D I would only have room for one sub $1000 lens, I would strongly consider going with a less expensive body to open up the possibilities on the lens side. Something like the Canon Rebel T3i can be had for a lot less and the image quality closely approaches or even matches that of the 70D and 7D. (This assumes autofocus during video shooting is not a big concern. That is the biggest selling point, in my opinion, of the 70D over a current Txi Rebel.) The Rebels don't handle as fast as the 60D/70D/7D, but the sensors are very similar. The $600+ you would save vs. the 70D would go a long way towards opening up the possibilities for a couple of good lenses. Something like the EF-S 17-55mm f/2.8 IS + EF 70-200mm f/4.

For most advanced photographers, there's no substitute for fast glass. That means lenses with wide (low f-number) constant apertures. In the case of zoom lenses the starting point is f/2.8, which allows twice as much light into the camera as an f/4 lens, which in turn allows twice as much light as f/5.6. For each doubling of the aperture, the shutter speed needed for the same exposure can be halved. If you can take a shot at 1/500 second at f/2.8 and get proper exposure, you would need to change the shutter speed to 1/125 second to get the same exposure at f/5.6. The difference between 1/500 second and 1/125 second when shooting many youth sports is the difference between a sharp image and a blurry mess. The same can be said of family pictures taken in indoor lighting. An f/2.8 lens may allow a shutter speed of 1/125 second that is fast enough to capture posed family shots. An f/5.6 lens would require a 1/30 second shutter speed, which would probably introduce blur from subject movement and maybe even from camera movement depending on the focal length and your Dad's physical condition.

In terms of lenses, it is almost always more economical to get better optical quality by purchasing two lenses to cover a wide focal length range than it is to spend more on one lens that covers the entire range and delivers lower optical quality across that entire range. This is true in the low end consumer lens range, but it is also true in the higher end pro lens range. The best EF 70-200mm f/2.8 IS II lens easily out performs the similarly priced EF 28-300mm f/3.5-5.6L IS in terms of optical quality at common focal lengths, and also has a maximum aperture two stops faster on the long end. In fact, the EF 70-200mm f/4, priced at about 1/3 the price of the other two, performs better optically than the 28-300. With the extra $1600 (70-200 f/4 vs. 28-300) you can buy a very good Tamron 24-70mm f/2.8 or Canon EF 24-105mm f/4 and even squeeze in an EF 1.4X extender to take the 70-200's reach out to 280mm. (The pro lens comparisons assumes a full frame, rather than APS-C camera. But the principle is the same.)

One final note: Avoid the EF 75-300mm telephoto lens, it is not a good lens. For an APS-C body such as the 70D, the EF-S 55-250mm f/4-5.6 offers optical quality comparable to the more expensive EF 70-300mm f/4-5.6 at half the price.