Children's play area with sand and mud

What tips would you give me? Especially for preparing the base? How deep do you dig the sandbox? What do you put down there that lets water out but keeps weeds out?

We took a ring from the sewer pipe, buried it, with a thick weed barrier fleece from the hardware store at the bottom. It is absolutely water-permeable, although the sandbox is not covered, even during this continuous heavy rain when everything around Cologne was flooded, there was never any standing water inside.... For the sand we used a perfumed sand from the hardware store that is supposed to keep cats away. That seems to work for two years now, because although we have stray cats and sometimes find droppings on the lawn, there has never been anything in the sandbox. Overall, it was a very cheap installation, the ring was leftover and the fleece with the sand probably did not cost more than 50 EUR, but I don't remember exactly.

perfumed sand? There is everything.
with us, it is washed Main sand inside and that's it

Our grandson's sandbox has only one section and in good weather, half a bucket of water is placed inside and refilled every 10 minutes. It is covered with a trailer net.