If the light trails are not rough (but paved?) then perhaps a recumbent trike might serve, tho' this would obviously make anything other than paved MUP-type trails out of the question. A recumbent seat would obviously give more back support, but might leave your back open to jarring since you couldn't raise yourself from the saddle.
It would also be much more expensive, so much depends on your budget, which, with 3 girls, is probably not generous..
Alternatively, a full suspension mtb might help protect your back and, given that you will only be riding light trails, you would only need relatively short 3"/4"/100mm suspension