We did this trip back in 2014, when F was almost 10 month old. It was our second overnight backcountry hiking trip with a tent since F was born. The first one was a weekend trip to Tricouni Meadows. Below are a short trip report on our thoughts just after the trip.
It was an 8 day (unsupported; no food pickups) backpacking trip. We hiked from Mammoth Lakes to Yosemite Valley by (mostly) the Pacific Crest / John Muir trails, about 50 miles / 80 km. We usually hiked 4-5 hours a day - basically during naps with a bit of awake-in-the-carrier time before and after - and took a huge lunch break so the little one could roam around, splash in water, try and eat pinecones, etc.
We was really happy with how the trip went - I think the little one had a fantastic time. Probably she won't remember it, but hopefully it will help form her personality somehow. I will certainly remember it, in any case, and it was great to spend so much one-on-one time with her.
The only thing I would do differently was food packing - we did a lot of freeze-dried (rather than dehydrated), which means more bulk, which means more (heavy) bear canisters - we had 4! Also, we brought too much food in general - we did our standard 1 kg per person per day... this has worked great on long expeditions in the past where you're working hard 12 hours a day... but with the little one there was way less metabolism. We forced it down, and still had at least 1/3 of our lunch food left over.
I don't regret the decision not to do a food cache in Tuolumne meadows, as most would do along this route, as I think it was a good one based on what we knew at the time and allowed us extra flexibility in case the trip turned out differently... but, if doing the trip again now that I have more baby-hiking experience, I would totally do it - it would have dropped 25 lbs of food and fuel from my pack. Kids grow up fast, though, so I guess very few have the opportunity to get really good at baby-hiking.