When we are talking about safe to use with babies and small children we are talking about the toxicity of the materials used, and specifically in relation to the component that makes the protector waterproof.
Of course there are mattress protectors with no waterproofing at all, but they aren't really mattress protectors because without the waterproof element your mattress will still become marked and stained and a non waterproof mattress protector isn't really doing much other than maybe creating a padded comfort section between you and the mattress, liquids and moisture will still pass through.
So to protect your mattress a mattress protector has to have a waterproof layer. This is usually in the form of either and pasted on waterproofing or by bonding a waterproof membrane to the underside of the protector.
The crucial factor comes down to what this waterproof layer is made from as some materials are safer than others when it comes to use with babies and small children.
So before buying anything look at what that waterproof layer is made from.
Is it made from either vinyl or PVC (Polyvinyl Chloride)? If so walk away and choose something else. For a start vinyl based products are not breathable so that will make the child hot and sweaty. Secondly they can be noisy and rustly and could disturb their sleep. However more importantly vinyl based products can be toxic and could release dangerous gases, so completely avoid PVC or vinyl backed products.
You will come across a lot of mattress protectors that have a backing made from PEVA or EVA this is Polyethylene vinyl acetate and Ethylene vinyl acetate. These were introduced as a low cost alternative to PVC they are better than PVC but are still best avoided as they still may contain chemicals that are unsafe.
The safest waterproof membrane is made from PU (Polyurethane). This is completely inert and safe in its finished form and is breathable, meaning thjat it doesn't make you sweat and it is soft and quiet in use. There are still some areas that you need to be aware of. Notice that we said that PU is completely inert and safe in its finished form? Well some mattress protectors have the PU applied to the underside of the mattress protector in a wet liquid form that then drys and sets. Polyurethane in its liquid form is not safe, and it dries and cures it is, but whilst it is curing toxins can be absorbed into the upper surface.
If the PU is bonded to the upper surface as a seperate already complete membrane then there are no toxins there to leach into the upper surface. So for complete safety choose a PU backed mattress protector that uses this method and not the liquid method of application.
But how do you know? The simple answer is that you don't know. The liquid method of application is a much cheaper process, so if a PU mattress protector seems cheap, then it almost certainly has used the liquid application process and should be avoided. Also if the manufacturer doesn't specify the method used then it is probably the cheaper method.
The other way to be sure is to choose a PU waterproof mattress protector that has been independently tested for the presence of harmful chemicals. Oeko-Tex is a european safety standard for a wide variety of products, including mattress protectors, so look for one that has been independently tested and approved by them.
So which mattress protectors meet all of these standards?
Snugnights manufacture Allergon and EcoSleep, both of these use a PU waterproof barrier. This has been applied and bonded to the underside as a finished seperate membrane. They have both been independently tested by Oeoko-Tex and awarded their Standard 100, which means that it is suitable for babies and young children and are free from all harmful chemicals.
An added bonus is that they can both be machine washed at temperatures up to 90c for complete hygiene and then tumble dried if required.