I dont think the 2 year old would have to pay so thats one plus.
A lot of the jokes might get lost on the 5 year old, but he/she would still enjoy it over all.
Probably a perfect time to go, otherwise you would technically have to pay for the younger child in the future, and it may be 2 or 3 years until the 2 year old can appreciate it enough to justify the cost.
Went in August with two 5-year old twins and a 2-year old. The twins actually got a number of the jokes and watched everything. The 2-year old watched almost everything and was fascinated with the activities involving the actors coming to the tables, and all three liked scraping the metal boards during the exit song.
Went a couple of years ago with 2 grandchildren (a girl and a boy-cousins not siblings) who were both 6 at the time. The boy was picked to be part of the show in one scene and he was over the top thrilled. I have to say the girl was not happy that did not get picked and there were a few tears-easily taken care of with a promise of a special treat. All in all, it was a blast. That was I believe the fourth time we had gone, the first time my kids were around 10, it just never gets old.