Hi Poldo,
I have the Audiovector Si3 Signatures - fabulous speakers.
But... I have 4 and 5 year old kids. You are right to be concerned about the stability - pariticularly on the spikes supplied.
My son when 3 1/2 managed to topple one of the speakers. Hasn't happened since but we have had to be really careful how they are placed in the room - not ideal acoustically but safe.
I am also a paediatrician - so there was no excuse....
With a 15 month old kid, very difficult to ensure they are away from the speakers (or any speakers!). I would suggest that if you do buy the speakers, you will need to put a barrier in front of them. Come to think of it, with any kid under around 4, a barrier is probably a good idea to prevent pencils being inserted into the drivers!
If you can sort out some kind of barrier, the AVs are well worth it!
Cheers,
EO