FourArms - don't know how old your children are - but I recently went on Holiday with another single mum - between us we had
4 children (aged 14 months, 21 months, 4yrs and 7yrs)
2 pushchairs
1 suitcase
1 large rucksack
1 large cooler bag
1 medium sized bag (over shoulder sports type thing)
2 tiny rucksacks (carried by the older DC)
2 changing bags
We took the train, about 5hrs travelling, 4 changes - you'll be able to do it (and if you do struggle I'm sure one of the rest of us will be able to help