Howdy, Maria! Thanks for bringing your question to the Disney Parks Moms Panel!
I can only imagine how excited your nephew must be about your upcoming trip to the Disneyland Resort! My daughter has always been very tall for her age. So much so that she went on her first big roller coaster at 3 years old! We never had any trouble entering the parks when she was 2 years old and didn't require a ticket. You might be asked how old your nephew is, but that is it. You should have no problem at all!
One area that you will definitely want to spend some time with your nephew in is Mickey's Toontown. He will have so much fun exploring Goofy's Playhouse, Donald's Boat, and Chip n' Dale Treehouse. Also, since he's tall, he might be able to ride
Gadget's Go Coaster which has 35" height requirement. This little roller coaster is actually super exciting yet tame enough for the smaller riders. It's also the perfect ride to introduce little ones to thrill attractions if they are up for it. Also in Mickey's Toontown are
Mickey's and
Minnie's houses! You can walk through and discover all the cute rooms and even meet Mickey and Minnie right in their own homes.
For an extra little bit of magic, head to Mickey's Toontown a few minutes before it opens which is generally an hour after Disneyland Park opens for general admission. Often, Mickey, Minnie, Goofy, and Donald will come out and greet Guests and even usher the little ones inside hand-in-hand to open this part of the park. It is SO cute!
I hope you and your nephew have a fantastic time at the Happiest Place on Earth!
-Linda