I don't want to sound too negative, but it is time for a reality check. A 400 miles self contained foot march is about 2-3 times further than what you would expect from military Special Forces on good flat terrain in good ambient temperate weather conditions.

Individual MREs only have around 1200-1300 Kcal in total. Individual entrées when stripped from the MRE package may only contain 300-400 Kcal. Complete MREs are heavy weighing an average of 1.7 lbs each. They are only really useful for a mechanised military!

Even bicycling for someone who is unconditioned may struggle to get 30-40 LSD miles per day. 400 miles on a bicycle + Childrens trailer could become a 10-12 day trip requiring at least a minimum 20-25 MREs.

An Electric Bicycle retrofit conversion wheel/kit or Electric Bicycle and a Powerfilm F15-3600 60w Folding Solar Panel or two could help considerably with the effort in good sunny weather on flat roads but this would be quite an expensive solution.