Depends where you go - the kidnapping risks isn't universal, just as terrorism risk in central London is probably very different from the risk in Pitlochry.
Took my kids when they were nearly 4 and nearly 2 to Moscow last September when I thought we were going to be moving there. With older kids, the non-buggy-friendliness of the metro, other public transport and the broken pavements and underpasses will be less of an issue. That said, there are quite a few children's options there, including kids' theatres, the zoo, big parks and fairground (in Gorky park), lots of museums.
Depends where you're looking at going and what kind of things you like doing. Lots of big spaces for running around in Moscow and St Petersburg (and probably in most cities). Also huge expanses of rural areas, but not a great infrastructure in terms of international tourism support and, outside the 2 big cities, probably a relatively low level of English spoken.
So, as with anywhere, you need to decide what kind of holiday you want before you decide whether it's for you. You should also bear in mind that it's quite expensive, especially in Moscow, and that's just accommodation, not counting the visas for which there's no child discount. We paid £300 for all 4 of us just for visas.