Mama koala OSFM fit my boy from 6w until he toilet trained at 2y3m just under 2.5. Most kids unless they are 90th perc+ should only need osfm but Losfm do exist for 3-5yr olds. I think for you a stash of 40-50 should be good for 3 kids. You will save so much money esp for the baby who will be in nappies for at least another 2yrs (I tend to train around the 2yr mark) Follow some cloth mamas on IG and Clean cloth nappies FB group which suggest a 1-2 day prewash and a 3-4 day main wash so because I was using night cloth as well (so Ft) I prewashed daily, and main washed day 4 as that’s when it was a full machine for me then I dried, so I dried only twice a week.
As well as the cloth diapers, if you change over to cloth wipes not only will you also save a ton in that aspect but you’ll never ever run out of wipes again I mean as long as you keep up w the cloth washing, add a handful of wipes to each load and you’ll have a forever supply of wipes there. It’s estimated that per kid uses 6000-7000 disposable diapers and 22,000 wipes, per kid. Times that by 3 and that’s 66,000 wipes bought used and wasted in landfill. So if you’re going to make the diaper switch I recommend you get a set of 70-80 cloth wipes as well. You can get both the Mama Koala diapers (comes in packs of 6, 6-7 packs will get you 36-42 diapers) and the wipes from Amazon.
We were gifted GlowBugs and their inserts. We started using them around 6m when he was bigger. We like them a lot.
I used alva baby with 2 of my kids and absolutely love them! Started my 3rd and last baby in cloth around 3 months when she was finally big enough to fit them.
My son used reusable from 1 to 2.5yo. Then we switched to pull ups disposable as he was potty training. Brand we used were bambino mio and littles and bloomz. Found the latest to be cheap but very nice. I bought almost all of the insert second hand on vinted/Facebook/thrift shops as the more they are used the more absorbent they are and didn't want to spend the first wash just to wash them to make them more absorbent. I think in total for all his nappies I spent less than £100