Tell your friends not to worry, there is plenty for children of those ages to do, especially at MK, but even at the other parks they will enough rides plus shows, people watching and everyday excitement to experience. When we went last year, my son was 2.5 and daughter 4.5 years old. At first glance, it can seem like the princess stuff dominates everywhere, but really there is soo much else to explore. Here are the things I'd do with boys those ages:
MK
- Meet Mickey! This was a highlight for my son, even though we did other character M&Gs and meals, Mickey was the only one he really talked about.
- Any boat ride, except POC which was too scary for my kids and we probably should have skipped
- Tomorrowland speedway, Dumbo, PPF, Carousel, Barnstormer, WtP, Ariel's adventure, Peoplemover, Aladdin's Carpet
- Tom Sawyer Island (I can never seem to fit this in since the hours are odd but I think its great for young kids to run some energy out)
- my kids loved the playground inside Dumbo and we spent at least 15min there playing, depending on the weather there is also a splash area nearby
- shows: Tiki, Philharmagic, Country Bears - depending on how active they are, they might not want to sit still but these are short and engaging, and can help induce naptime
- watch the Muppets in Liberty Square, I think my husband and I probably enjoyed it more, but there is a re-vamp of Muppet Babies on Disney Jr so they may know the characters vaguely
- Riding on the railroad was big for us, but I think it is currently closed. If it is parked in view anywhere, it's at least worth visiting for a photo op.
- Peter Pan, Winnie the Pooh/Tigger, Gaston all meet outside their rides/areas, maybe Mary Poppins, Tinkerbell, or Princesses if they are familiar with certain movies/characters
- Street Dance Party has some unique characters like Nick & Judy from Zootopia and the Genie from Aladdin
- At those ages, fur characters can be good or bad. My son was pretty hesitant, not full-blown screaming but he wouldn't be in a picture without me holding him. The princesses and other face characters were fine though.
- Pirate's League is an option if they are into dress up/pirates/face paint but at those ages I think it'd be a waste of time and money honestly since there are so many other things to do in MK
At Epcot: Future World has the most options, there is something for kids at each pavilion in my mind
- The talking birds outside The Seas was a huge hit. We rode the Nemo ride at least 3 times plus all the fish tanks, we spent at least 1 hour here. Turtle Talk will probably go over their heads though.
- Character Spot or Disney Visa M&G
- I think there are play areas at end of Mission Space and Test Track that may interest them, so one adult can stay with them there if you are doing rider swap
- WS has a newer suitcase ziploc bag thing for kids, free activity passport basically, it is cute and they can stop and color and get a card at each country, didn't really keep my kids' interest at such a young age but can help occupy them if others are wanting to tour. Also, the miniature trains in Germany and boat ride in Mexico are winners.
- we also did the Bon Voyage breakfast at Tratorria al Forno in order to meet some Princes with the Princesses.
AK:
- Dinoland and Festival of Lion King, Safari, walking the animal trails and walking through Pandora, Nemo show if you have time. Skip ITTBAB. Shame that they closed the train to Rafiki's area, that was my favorite
HS:
- Toy Story Land, meet Olaf, Frozen Sing Along, Muppets show, Disney Jr show and meet Characters (i think it's Doc McStuffins, Sofia and Vampirina currently), unfortunately there is no PJ masks or Puppy Dog pals which are the two shows my son loves.
Definitely agree with taking an afternoon break, especially if y'all rope drop. Even with an afternoon break, my kids were exhausted by 7 or 8pm, so your friends may need to plan to exit early and skip nighttime shows if they feel the kids can't last. Pack plenty of snacks! My kids are generally happy to sit in a stroller while the adults ride rides, shop, etc as long as they have something to eat. My other recommendation would be to plan pool time if the weather permits, the one thing I've learned in life from my nieces and now my own kids, is they want to swim whenever they see a pool, even if they have one at home! No matter how many fun things we do on a trip, they are always begging to go back to the hotel to swim!