Hello, Mamagug, and welcome! No one is out of their element here, we all started somewhere!
Not sure actually how you could create that much texture on a flexible surface that the kids' handprints would indent into (if I understand your intent). It would be easy to do colored handprints with paint, but not sure that's what you envision. My concern would be that a flexible surface like canvas would cause any heavy build up of texture to crack...
You could try doing this on maybe a more rigid surface like MDO (sign shop would be able to help you with Medium Density Overlay), or MDF (Medium Density Fiberboard, if it will not be exposed to moisture). Depending on how big you want to go, weight could be an issue. Then, once you lay on your texture, the kids would have to press their hands into it before it was dry to make the impression.
There are plaster hand molds, that I'm sure you've seen (my nephew "made" one for me years ago, but it's small and heavy for its size).
If you went the "easy" way, paint handprints could be made to LOOK indented by adding a shadow and highlight with a brush after the print is made by the child. I could show you an example if this interests you. This would be a "trompe l'oeil" (trick the eye) effect, with the canvas actually being flat but painted to LOOK 3 dimensional... an effect I love
Hope this is of some help, and maybe someone else can chime in with better info...