Don't worry yet. Especially if they're bouncing about. Plecos can be pretty sensitive to change and being moved, and some will go for a while without eating. However, yours are bouncing around and likely eating algae and tiny waterborne organisms off the glass and wood. Just because you can't see the algae yet, doesn't mean it's not trying to pop up! Also, they will nibble on the driftwood too, they need that to aid in digestion.
Now, for the zucchini, did you blanch it first? If not, you need to. Freezing can do this for you, or you can boil it and then pop it in the fridge or freezer. What I do, because the stuff doesn't last long otherwise, is I slice it, pop it on a flat sheet with wax paper and then freeze it overnight. After that I brush it all into a ziplock bag and freeze it. I take out bits to defrost, I do so with hot water in a bowl for several minutes until it's squishy, and feed. I also like to remove the seeds in the center so they don't choke. Typically I do this when I slice them. =)
Try popping in a little brine shrimp or mysis which is better from time to time, glassworms are good too. My baby BN's like Emerald Entree, you can buy that at most pet shops in the frozen food area. Good high quality veggie flakes can be sunk in for them as well. They need a bit of protein in their diets too, not just plant matter, since they are catfish, so don't forget. If they don't go for it after ten minutes or so, or when they've eaten for several minutes, I usually suck out extra food with a turkey baster. With bottom dwellers you gotta let stuff hit the bottom and stay for a bit. I usually leave zucchini in overnight, rarely have anything to suck out after that. lol The rest needs to be yanked out after a few minutes or it hurts the water quality, you can wait until they lose interest if you want, but that can take a while since some will actually sleep on the left overs! lol
Just in case, check your water parameters. If you don't have a liquid test kit, I suggest you nab one. They're costly, but often the most accurate, strips being on the bottom of the useless list there so don't use 'em. Make sure you have no ammonia or nitrites, and low to zero nitrates(usually safe up to about 20ppm, after that if it's spiking it can bother them). And also to be safe, a small water change can't hurt. =)
Make sure you have enough room for them, even baby plecos have a pretty high bioload, though they're not nearly as bad as some species of pleco. Six of them would need 55+ gallons, under three inches or so you might be able to pull it off in a thirty gallon for a very short time, but I wouldn't recommend it since even the smaller BN's can stunt if there's not enough space and other fish hanging out with them. I have five babies in a 73 gal pool, they love it and man are they growing fast. They were about an inch when I got them a month ago or so, and have grown about an inch since. :3
OH! Forgot to mention, sometimes they wont come to eat during the day. Many plecos like to feed after dark and will minimize grazing during the day. Youngsters will especially, they're used to dad toting them around safely(of course this usually wears off after they're big enough to be sold, so I assume your babies are at least two or three inches). So try feeding them after lights out, they find the food very easily in the dark. =)