A trick for getting prefolds nice & tight:
1) Fold down the back a bit if the rise is too long. This makes it easier to put into a cover too. The rise is too long if parts of the prefold reach or go above the belly button.
2) Lay baby's bottom so that the end of his bottom is just beyond the folded down part/the back part of the prefold is above the hips.
3) Fold in the front ends of the prefold towards the middle. So take the right part and fold it onto the middle 'soaker' part. Then take the left part and fold it over on top of the right part.
4) Bring up the legs. While gently pulling on this end, use your middle fingers to slightly flare the top. This should move the two parts you folded on to the soaker apart a bit.
5) With your Right hand, hold down the now flared top part (I usually rest my thumb on the 'left' (for you) flare and my pinky on the 'right flare.
6) Using your left hand, grab the left edge of the back end of the diaper and put it on top of the left front flare, putting your thumb on it to hold it together.
7). Using your left hand, grab the right edge of the back end of the diaper and put it on top of the right front flare, putting your pinky on it to hold it together.
For step 6 & 7 you need to move your right fingers off just before you bring the edges together. Similar movement to how you flare out your cards in a card game.
8) Using your left hand, latch the left part of the snappi onto the left 'wing' you just made, letting go of it with your right thumb as you do so.
9) While stretching the snappi across your baby, hook the right end of the snappi onto the right wing.
10) Then pull down the lower end of the snappi.
Now, for the
2 TRICKS to getting a tight fit:
Trick 1:
Roll baby on his right side a bit and start tucking in the back edge of the prefold. You want to use a bit of a curling tucking motion (similar to rolling a tube of paper--you push the paper in, but in a downward curvy motion). Do the same on the other side. What this is doing is creating a barrier to poop. It's a raised edge. It also tightens the rear portion a bit, and exposes more of the upper thigh--both good things.
Trick 2:
This is the one I haven't seen before, but it literally makes a huge difference in fit. Lay baby back on his back. Using your right thumb, unhook the snappy (using the finger loop). Hold it taut though, With your left hand, pull up the front of the diaper until it's a bit tighter. Hold down with right index finger. Using your left hand, pull on the back wing so that you pull it more forward. Re-snappi.
Repeat on the right side. This takes up ALL the slack that might be at the front of the diaper.
At first it might seem like it takes 'forever' to do it, but now it takes me 20 seconds with a squirmy toddler. It took me a while to figure out trick #2, I was still having some poo explosions on toddler poop (thankfully our covers caught all of them).
-----------------------------------------------------------
For leaks, you need to look at fit. Once you put on the cover, run your hands across the back and front of the diaper. There should be
no prefold/insert sticking out.
Look around the thighs, make sure all parts of the prefold are covered by the cover. If not, 'tuck' the prefold in using your fingers. This part is really helped by trick #1. The tighter you roll the prefold in, the higher the thigh line, the less likely anything will be sticking out.
To check legs, grab your baby's legs and 'pump' them (looks like you're helping them with gas). You don't need to be vigorous in it, but it
will expose if there are any gaps. If, during the pumping the cover shifts in such a way that you can see the prefold, even if just a tiny gap, it WILL leak.
Or, you might see 'wing droop' where the front of the cover migrates downwards at the sides. This can expose the prefold at the edges, causing leakage.
Solution: Different cover style.
-----------------------------------------------------
Pee leakage:
I've had issues with pee too. Here are three reasons & solutions I've found:
1) Not enough absorbency.
For longer naps or longer outings, you might just need more stuffing. Also, ds pees too much for an infant prefold. I had to move him up to premiums, even though he still fits in the infant prefolds. You might have to size up or get more 'layers' in using doublers. A cheap, yet a bit bulky, doubler is a flat/receiving blanket folded down into a rectangle and layed on top of the prefold.
2) Wrong cover for baby shape.
My son has gone from a super chunk (6 mos and 22 inch waist--NOT joking) to a 2year old who, width wise, fits into 12 month clothes. He's chunked up a bit and is in 18mos width wise right now. He still has really skinny legs. His thighs are 11inches.
For a super chunk baby, you need to get a cover that's more generously sized. Proraps are thicker in the thigh area.
For a skinny legged baby, a side snapping cover helps a ton. These also work on chunky legged yet slimmer waisted (proportionally) babies too, since you can adjust the legs independently of the waist. A good (inexpensive) cover is the Mother-ease Air flows. No marks & leak proof.
3) Going too long between changes.
If ds has finished a cup of liquid, he needs to get changed withing 10 minutes. He will soak the diaper. Happens in sposies too. A wet prefold/diaper is like an overly wet sponge. Any sort of compression (walking, sitting) will squeeze out liquid. And no matter how great the cover, it's not made to hold a big ole' river of pee.

Ami