My youngest DS had this when he was 6 months old back in 1997. He had a few days of blood in his nappy, going a very strange mottled grey colour, crying in pain and a sweet pear drop smell on his breath. GP did not take it seriously, said he had a tummy bug. Took him to A&e on the Friday night and waited 5 hours for a paediatrician for them to say he had a tummy bug. Blood looked like cranberry jelly in his nappy which is a classic sign.
On Monday morning I went into his room and thought he was dead :-(. He was a horrible grey colour and hardly moving. Took him straight to A&E and they rushed him straight in and put him in isolation as they still said he had an infection. My gut instinct told me it was something more sinister and after a few hours of only checks being made by a nurse I stood out in the corridor and yelled for a Dr, would not speak to any nurses until a Dr came. A fabulous South African Dr came straight away, asked what his symptoms were, I described as above, she asked me if he was a second son and about 6 months? She had apparently just been reading all about intesuception (sp) and said my son had all the signs. She checked his abdomen and said he had to be transferred straight away to GOSH.
We were blue lighted there and it was a horrendous journey but there was a team standing by as we pulled in. The Dr there felt his abdomen and confirmed the diagnosis. The plan was to blow air up his bottom (think its called an air enema) to try and unblock the bowel. They wiuld try this 3 times on 3 different occasions and if it did not work they would have to operate. Fortunately it unblocked on the third go of the third attempt. We were kept in for 5 days of observations before going home on Christmas morning.
Unfortunately it reoccurred 17 days later (very rare) and we had to go straight back to GOSH but it unblocked on the first of the three times. We were kept in another 5 days for observations but then allowed home. No problems since then.
It was very frightening at the time and not many people knew about it then and there were only 3 hospitals in the UK at that time that could deal with it.
Hope that helps in some way.