Not really, but the creaminess of the yoghurt just tempers and smooths any acidity from the tomatoes and paprika and gives the sauce a really good creamy texture. Unless you are cooking at the Hungarian School of Great Britain, I doubt your kiddywinks will know any different - they'll just think it's a lumpier bolognaise than normal, especially if you're serving it with noodles................................
If you still want to add the yog, though, you can use Greek yog, which is much better tempered than just plain yog. In any case, use a full fat one, not a fat-free - you're less likely to get curdles if you use a fat one. Oh, and don't have the sauce boiling when you add it (if you do), as it will certainly curdle then!