The question really isn't about size, it's about season. What type of palm do you have? They should be fed just before active growth begins, generally in early spring.

Have you potted them up into separate containers now? When they start to grow next year put them into fresh compost in a size larger pots and pot on into fresh compost as they grow big enough to need it. No point in feeding them if they are in fresh compost and growing well so difficult to answer the question without more details or a photo.

Hi, welcome to GoY, I agree with Steragram, as they're seedlings, which will need a few years of potting on, there will be no need for feeding, but can you tell us what palms they are ? on your question it says on plant palmeradiabanico, but there is no such palm, but whatever it is, it makes no difference to the advice given, Derek.

Makes a big difference. The question says nothing about seedlings - that's what you infer. But even seedlings need to be fed to grow big and strong. If you are using fresh compost, it's there already. As I mentioned, it's best to do this just before active growth in the Spring. Don't bother them now while they're resting. And this...

'Most landscape palms will require fertilization once or twice during the growing season. Not just any fertilizer will do, however. Palm trees have special needs that must be met with specially formulated fertilizers that target specific nutrient deficiencies. Homeowners should also apply regular maintenance fertilizers to healthy trees.'

Full Article:
https://www.treehelp.com/fertilizing-a-palm-tree/

You don't say where you are in the world, nor how tall your plants are at this stage. If you're in the southern hemisphere, they can be fertilized now, in theory, if they are big enough, but since we don't know just how big they are, its hard to say, since they could be anything between 3 inches and a foot or larger in height.

'Palmera de abanico mexicana' appears to be the Spanish name for Washingtonia robusta; is that the plant you mean? and perhaps you are in Spain? In which case, if you're growing in pots, fertilize next year every two weeks, see link below

https://m.wikihow.com/Grow-a-Washingtonia-Robusta

Aha, I've just seen your previous question, where you mention they are five inches high ... if you are in the northern hemisphere, do not feed them now, wait till the growing season starts again next spring...

So you see why it helps to put your location on the profile on your home page - helps us to give an appropriate reply for where you live.

Giving the location & plant name would help, but it's also important 'for us' not to infer or assume we know information that isn't given. Then we are off in another world. That's why I said 'just before active growth begins, generally in early spring'. This would apply to all hemispheres.

Thanks Bamboo, never thought about splitting the word up, Derek.

I didn't really think about it Derek, I just started painstakingly copying that name into Google, making many mistakes... and Google offered that up as an option when I got to 'de'.... I thought it might offer something though, if it was a plant name of some sort, it usually does. Not always accurate, but a useful guide at times...

That's funny! Thanks Bamboo & Derek☺

Paul - did you notice the question was asked twice? The other version of the question said the pants are 5" newly grown seedlings...

I noticed it after i typed all this. It didn't help much lol!

Thompson, palm feeding schedules depend strongly on circumstances. If Bamboo is right in her surmise--and likely she is--that these are Washingtonia robusta seedlings, then the following patterns might be useful.
Seedlings grown in a standard sterile seed starting mix will need frequent, light applications of liquid plant food, of near 3-1-2 proportions, from the time the seeds were sown, until they are transplanted into pots more than 8 inches (20 cm) wide. If the seedlings were started in a compost-based mix with a high nutrient content, feeding starts a month or two after the seedlings emerge.
If growing in a warm greenhouse, or outside in a tropical climate, nutrient needs are constant. If growing outside in a subtropical or warm Mediterranean climate, feeding is only needed during active growth in the warm season.

Ah well, Tug's the man who knows what's what...

That's right and he elaborated on what I said in the first reply

Sorry, Bathgate. I should have given you full credit, but I had to run and find out what my cat was into--again!--and I lost my train of thought! He wandered off in the direction of my sister's bedroom, and, when I heard ripping cloth, I ran for it! When I came back distracted, I just posted it as was.

Well I don't know where my cat is, but I hear him. He's pitch black and so is my house at the moment so it's black on black on black. I wasn't looking for credit or anything, I'm just trying to reply to Steregram even though I have no idea what her point is. I know you're smartest one here. Good Times!

Is anyone else doing what I'm doing... LMAO! I do like a good laugh...

Yes, indeed I am, Derek.😉😄😄😄

Me too LOL! Truth is stranger than fiction!