So, let's take this one step and one issue at a time.
Cloth Diaper is leaking at the legs with big wet spots.
Potential Causes & Solutions
1. My first thought would be gapping. If this is happening to your baby, check to make sure you have a good secure fit around the leg. If baby sits up, or spends time in a bouncy chair, check the diaper then. Some times the change in position can cause gapping if the diaper is not on securely enough, or if it is too big for baby. If the diaper gaps and baby pees, well...you get a wet spot. If gapping is the problem, readjust baby's diaper. If it secures with velcro, angle the front tabs downward in a v in the front providing a more snug fit in the legs. If the diaper closes with snaps, use a smaller setting to provide a tighter fit. If neither of these solutions solves your problem, the diaper may be simply too big. If this is the case, I recommend tucking it away for a few months until baby grows into it. Remember size charts are not perfect. They represent an estimated weight that a diaper will fit your baby.
2. Second possibility is that the diaper does not have enough absorbency for your baby. Your baby may be peeing more than you realize and he may be saturating his diaper, causing it to leak. The solutions to this problem are pretty easy. Solution 1 is to add a doubler if the diaper is a prefold, Fitted, or AIO. Solution 2 is for pocket diapers. Add a hemp insert or hemp prefold. Most pocket diapers come with microfiber inserts. Microfiber is fast absorbing and very absorbent, but hemp holds a good bit more and is even more absorbent. Find doublers and inserts here.
3. Next possibility would be repelling from detergent build up. Detergents with optical brighteners (Free & Clear detergents are notorious for these) tend to cause buildup on cloth diapers. This is not harmful, but it will cause the diapers to eventually stop absorbing. If that happens to your diapers, you need to strip them to get the detergent residue off.
Usually these 3 steps will remedy cloth diaper leaks. If not, email me: firstname.lastname@example.org and we will troubleshoot and see if we can figure out what is going on.