should I build a pedicab trailer ???

I am pulling my 2 granddaughters (3.5yrs + 5.5yrs) in a common 2 seater childrens trailer
I have been pulling them in one for 4+ years...3 with an engine (well over 6000 miles)
now they are getting bigger and I need suggestions or ideas on how to upsize their ride
I take both to school mon-fri and return home with youngest (I live with them and babysit while mom n dad are working)
should I think of a train type deal (2 trailers in tandem)?
or maybe a scaled down pedicab ?

any links to designs would be cool as well...so i can pick stuff that'll work for my needs

thanks for any help guys

thanks for the input guys...
I'm leanin toward a scaled down pedi-cab kinda trailer