Had to look up pami pebbles, never heard of them.

If kids are just walking around or playing in it I can't see where it would matter. The difference comes if they're potentially jumping or falling into it. There's a table that breaks down the various materials (link below)

Anecdotally, I'm not a fan of pea gravel for kids' play areas. We had a fancypants play area built when I was in elementary school and the flooring material was 5" of pea gravel. One got good at surreptitiously picking it out of one's legs during class post-recess to avoid getting sent to the nurse's office. No kid likes hydrogen peroxide.

Here is a link that might be useful: fall table, more info

If there is a fall zone, because the structure is elevated you should have engineered wood fiber mulch as a cushion and the depth of it is based on the height of the fall and the age group. If this is a playhouse sitting on the ground, I'd still recommend the engineered wood fiber mulch or you can get interlocking pervious epdm tiles which are clean, safe, and easy to wash. Peastone of any kind wouldn't be an option.