Awh, they just wanted a nice relaxing beach day in their cute beach outfits :'(
Pearl's Beach dress is something my grandma would totally wear.
How to tell this isn't canon: nobody in their right mind would genuinely think that Steven would do this. Yellow Tail would maybe make sense since he doesn't seem to be around much, except for the fact that Steven is someone Onion likes and talks about with his parents as shown in Onion Friend, in which case Yellow Should know that anyone who can earn Onion's respect is clearly an impressive individual.
You have an entire family of people working for you, one of which regularly has plenty of free time to hang out with friends, you can spare someone to help clean the beach. Preferably you, since it's so important to you apparently.
Sigh, but of course Steven would offer to do it instead, because everybody just spent ten minutes guilting him into it.
Oh come on, can't any of you offer to help?? Even if you're busy you can send out word to the town for volunteers instead of leaving it with the group who ALREADY have the full time job of PROTECTING THE ENTIRE PLANET!