Hello, fellow Washingtonian.
If you don't mind driving up to Summerlin and visiting City National Arena, that's where the Knights do their morning skate and practice. It's also where you've got the greatest chance to have your 5 year old get in close proximity with the players. City National is a pretty easy place to get to, and once practice is winding down, there's an area between the rink and the locker room tunnel where the kids can stand near the barrier and often get autographs/to meet the players. There's no real scheduled player availability, just get there in time for morning skate (depending on how the team is doing, you may have to show up early to guarantee a spot in the arena since it only seats 500 or so) and start making your way over to the cramped little area on the side opposite the stands. It's kids only, so you'll have to show them where it is and have them move their way up to the front on their own. There's no time to be bashful, and some of the local kids will have the jump on it since they've likely done it a few times before.
The doors to T-Mobile open an hour and 15 minutes prior to the puck dropping, and immediately prior to that, the Knight Line dummers, Chance, the broadcasters, and a decent contingent of fans march to the front doors of T-Mobile. They leave from around the front doors of Nine Fine Irishmen in front of the NYNY. If you'd like to participate in that, you'll want to show up around 90 minutes prior to puck drop. I personally think it's cooler to watch them march by and jump into the line following them, but you may have a shot of a little Chance time if you show up at the beginning of the march when they're getting everything organized.
You can go all the way down to the glass for pre-game skate regardless of your tickets, but again, the earlier you can get there, the better. If you follow the crowd from the march into the arena, you should be right on time. The Knights practice on the side of the arena with the castle, and if you can get closer to the tunnels (the bench/upside down center ice logo side) it seems like a better shot of getting a puck. If the goal is to just get close and watch them practice, there's a lot less of a crowd on the endboards, plus you'll get to see more Fleury/Subban.
If the weather is nice and you don't mind hanging out a little longer than normal post-game, you can walk along the parking garage toward Tropicana Ave and stop at the little driveway and see some of the players leaving to go home in their vehicles. It's less exciting than you may think, though.
The Park area outside of the arena will have free games like cornhole, giant Jenga, bubble hockey, etc. for free, and there's usually a DJ playing music to get everyone hyped up. However, there's a decent amount of pre-game bar activity, so you'll likely want to hang out on the side closest to Park Avenue.
If you're there for a few days, regular practices are also always at City National, and they'll likely have those the Monday prior to the game and the Wednesday after, so you can get an even better shot at getting some player face time for the kiddie. You can grab some food at the pizza place and make a fairly inexpensive lunch activity out of it. Summerlin may look far from where you're likely staying on the map, but it's a fairly quick drive. Plus, if the weather is nice, you can hit Red Rock Canyon afterward (10 minutes further down Charleston) and make a half-day out of it.
Let me know if you have any other questions, and I'm sure the other folks here will chime in with some more suggestions.
These guys have led you in the right direction with their all of their advice.
