We took our DD to a friends funeral when she was six months old, just because we couldn't go if we didn't. Although it's diff with a three YO ie more questions etc, it's the 'disruption' question we wrestled with. She did start making a noise half way through, but my DH just took her out while I stayed in the service.
The situation may be different if it's close family and I would be more inclined to take my DD along at 3 YO, but that's just my opinion.
we took my DS (aged 3) and DD aged 9 months to a family funeral. Very sadly the funeral was for a young woman so there were several children there (including her own aged 2) They had arranged for children to be at the back of teh church with carers and there were some toys there. We brought our own too. As it was a family member on my side, i sat at teh front and DH at the back with DS and DD. But it didn't work well as i don't think we had prepared DS. The atmosphere freaked him out and very uncharacteristically he started to throw felt tips around and was removed before the coffin arrived. I ended up taking a very hungry DD to burial (but didn't breastfeed until after) and then all went to the wake which was fine. We didnt' really have many other options as it was along way from home. The other children (apart from our DS managed fine though.
DS didn't ask many questions and i decided not to explain what wasn't asked given his age (just 3) and the horrible circumstances. but the next week he said ' I didn't like that church mummy' It wasn't fun for him but hasn't scarred him for life and we just explained that sometimes you have to do things that aren't that fun.