If the kid is too young and not too knowledgeable about the world then perhaps it would make sense to not be left alone with an -online- tablet. If the kid is older then parents should have by that time invested time and talked with their child and let it know of what dangers may await online.
Finally and with regards to the 'indecent'/'porn' aspect of the filter, if a child is traumatized after viewing a pair of boobs or a vagina then there is something wrong with the upbringing the parents gave to it. Having sexual education websites blocked by the filter makes the matter all the more worst.