I’m going to go out on another limb here - because I really want to help - so please don’t judge this, overreact, etc. - you can tell me if I’m climbing up the wrong tree, ok?? 
First of all, I want to mention that while some other parents - friends or schoolmate parents - may seem to have it all together and have the perfect perky happy situation at home - they don’t. MOST moms and dads have meltdowns at some point and find them frazzled many times during the week trying to keep up with the role of parenting. Some talk about it (you) some don’t (THEM!). You are not alone.
Next…I can fully imagine your scenario this morning with the Valentine craft. Fully good intentions, well planned out in terms of materials and all and very timely - Valentine’s Day is next week! Then, it rained on your perfectly executed parade - the boys weren’t interested and the activity seemed to be a fail. Ugh - as a parent, that feels awful.
Let me ask. Who are YOU? What is your personality? Are you uber organized? Over achieving as a person outside of parenting (in your life before parenting)??? Sometimes in our quest to do the best for our kids we over compensate in effort - or maybe I should say our efforts get parked in the wrong lot - what seems right on paper does not fly in real life. A next door neighbor 5 year old girl, or a next door neighbor 4 year old boy might have loved your craft set up - maybe it’s just not your kids bag - THAT’S OK!
Or…maybe leave the items somewhere accessible and your kids are more prone to go back to it during the week and maybe a few more Valentines. YOUR wheelhouse may be to set it up and get it done. Their wheelhouse maybe less structured - go back and revisit the craft station on their own terms. It’s something you can experiment with.