Limitations on kids and their collections.

Firstly forgive my lack of knowledge and experience here, I am really unsure of the boundaries and would love to here from more experienced people.
Taking my kids anywhere generally involves coming back with a collection of stuff. I took my 4yo to an open day at the local school (she starts next year) and she managed to come home with an armload of sticks that she collected in the school grounds. Typical pre-school behaviour.
So what limitations do you set on kids on walks. I mean I want to encourage them to pick up things, to touch and to explore - because that is an essential part of being outside. I also want to teach them about areas that they can't touch and things they can't do (and at 4yo she is very capable of understanding that in certain areas we can do things and in certain areas we can't). I know the adage " take only photos and leave only footprints" but that does not apply to everywhere does it?
When do I tell my child not to pick up sticks, or rocks, or flowers? Is it okay to collect sticks and rocks in national parks (but not flowers)? etc etc. I want my kids to understand the importance of conversation, but also when it is okay to freely explore and collect.
I know I must sound like I am asking a dumb question, but I am just really unsure. Thanks.
Taking my kids anywhere generally involves coming back with a collection of stuff. I took my 4yo to an open day at the local school (she starts next year) and she managed to come home with an armload of sticks that she collected in the school grounds. Typical pre-school behaviour.
So what limitations do you set on kids on walks. I mean I want to encourage them to pick up things, to touch and to explore - because that is an essential part of being outside. I also want to teach them about areas that they can't touch and things they can't do (and at 4yo she is very capable of understanding that in certain areas we can do things and in certain areas we can't). I know the adage " take only photos and leave only footprints" but that does not apply to everywhere does it?
When do I tell my child not to pick up sticks, or rocks, or flowers? Is it okay to collect sticks and rocks in national parks (but not flowers)? etc etc. I want my kids to understand the importance of conversation, but also when it is okay to freely explore and collect.
I know I must sound like I am asking a dumb question, but I am just really unsure. Thanks.