I need some advice and a discussion about, garden ponds.

I would like a pond in my garden, not for fish but for frogs etc... a proper natural pond, Not a large one perhaps, 3ft x 4ft ish at most.
I know this is a fantastic addition to a organic food producing garden!
the problem is, I have a toddler...he is 2, and pretty smart! I hadn't thought it would be an issue, given that I would teach him all about the dangers and safety etc...
Now I have mentioned this pond idea to my parents, one of whom is a paramedic! and they are dead against it, in fact they are so against it, I have had a talking down by my father! They are just too dangerous.

Of course I wouldn't dream of putting my son in any danger, so my question is...

Is it too dangerous for me to have a pond in the garden? and if so what age should my son be, before I do decide to go ahead with putting one in?
Any advice, opinion either way would be so helpful...
Thanks in advance

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