We have stayed in this campground on many occasions in the summer. Please read other reviews to understand how to make reservations for the summer... you must know the strategy!
We would love to stay in the higher number spots (189-240) because of the closeness to Happy Isles and the seasonal creek (fun play for little kids) but the spots go quickly. One downside to these spots is that there can be more mosquitoes due to the seasonal creek.
The middle loops (95-155) are mostly all great. We have stayed in several of these sites. Most are well shaded and provide plenty of room. The inside loop sites are generally smaller than the outside. One disadvantage is the farther walk to a shuttle bus (Happy Isles stop or Pines Campground stop).
The low number loops (1-94) are equally nice as the middle loops. The advantage is the closer walk to the shuttle stop (Pines Campground stop).
One other important bit of information: the lower the number of site, the earlier the sun rises on your site. We were cold many mornings in the higher number sites, even in August, and we eagerly anticipated the sun rising above Half Dome. Half Dome is also visible from the lower number sites but not the upper numbers.
Upper Pines Campground is set right in the midst of the grandeur of Yosemite Valley. The campground has soft pine needles, so don't worry about too much dirt. Some of the sites are right by a stream that is perfect for an afternoon dip if you're hanging out. Beautiful pine trees keep the campsites cool in the summer months. This is family camping at it best. However you must be prepared for some inconveniences. For one, you have to book the campsites at soon as they are released. 180 days before your planned visit. The campsites are also close together and and Yosemite valley is crowded with traffic most of the day during the summer months. Finally in the evening, be prepared for rangers shooting blanks to scare off bears. So be prepared for a disturbed night of sleep and crying kids if they get scared by loud noises. Nothing beats the convenience of Upper Pines, but if you're looking for a more peaceful setting, try Toulemne Campground which also usually has more last minute availability.
We have camped here numerous times and prefer late spring during the week days the most, since it is less crowded and the weather is usually nice. From the campground we like to hike up the mist trail to vernal and nevada falls. We also enjoy walking or biking out to mirror lake which is a nice flat walk or bike ride. We've also hiked up Lower Yosemite falls. We tend to stay out of Curry Village since we are there to enjoy nature, but there is a store in Curry Village as well as some restaurants. Bridal Veil Falls is also a nice place to go with kids as it's an easy walk to a spectacular waterfall. Kids love to hang out in the campsite riding bikes and exploring. There are so many trails and so many wonderful things to see, the valley is a treasure to be enjoyed!
We took our two year old and 4 week old camping in Yosemite and stayed in Upper Pines for two nights. We happened on a great weekend in September with warm days and night time temps in the 60's. Even though we were staying in a tent, the Ahwahnee Hotel is open to all Valley visitors and was a perfect place to hang out on the comfy couches and nurse the baby. The toddler and my husband hiked up to Glacier Point (toddler in the baby backpack) and sure got a workout. A few things I learned- a six person tent is perfect for a family of four with lots of gear, bring glow bracelets for the kids to wear at night so they are easy to see around the campsite, and don't count on your cell phone to meet up with friends and family- there is hardly any coverage with most networks. That can be a good thing!