Hi pblfive,
Post #2 here has links to all the better posts in the forum that talk about children and mattresses including some good information and links to some very good quality and value sources.
Since your children can’t test a mattress anyway (they would have no idea of what kind of feedback to provide or what would be best for them) … I would probably consider ordering a younger child’s mattress online unless there was some very good options available locally.
This is just a traditional innerspring / polyfoam mattress but it has no information about the density of the polyfoam. It does say that the polyfoam is CertiPur certified so for those that are comfortable with polyfoam in the comfort layer of their children’s mattress CertiPur would at least provide some assurance of lower levels of VOC’s and harmful materials in the polyfoam … although I would still want to know more details about the layers 9such as foam thickness and density).
Latex would be the least toxic of all the foams and would be my personal choice for a child (with wool in the quilting for ventilation and breathability along with a good mattress protector). I would certainly avoid any memory foam (for support reasons as well as possible sensitivity issues). If you are comfortable with polyfoam and you consider it to be “safe enough for you” … as long as it is either CertiPur certified or made in North America it would probably be “safe enough” by most people’s standards … although I personally would choose latex and/or natural fibers … especially in the upper layers
As long as the comfort layers on top have not developed soft spots or impressions then yes you can add a topper for extra comfort as they grow older and need it.
Phoenix