The family friendly sections are the off-road sections of the Ayot Greenway W and E of Wheathampstead.
A sharp descent out of Harpenden to NCN 57 0.4 and off on more Hertfordshire branch lines - the Ayot Greenway. - turn L Spinoff 11b to Luton. Sadly the rail track has to be abandoned 2; R for Spoke 12 to St Albans, L to continue on narrow and busy B653 for a mile to Wheathampstead.
Cycle Orbital recommends ignoring L NCN57 3.2 and continue S to enjoy the town and its facilities 3.3, regaining the cycleway after passing over the Lea again and an excursion through the town’s river park. The track doubles back under the bypass 4. R Sheepcote Lane Spin-off 12 has joined from St Alban's via the Belgic Oppidum and will continue N once both routes have climbed back to the branch line 4.2.
Ayot Greenway to 6.4 is a highlight section. At the road it’s R through Ayot Green (L NCN 12 to Knebworth), over A1(M) and 6.8 back on the branch line to Welwyn Garden City 7.8. At which point NCN 12/57 turn S through Welwyn suburbs and centre. This is a good alternative, especially if taking the train at Welwyn Garden City (if approaching the station from the east there is a footbridge entry from sideroads - porterage up steps).
Cycle Orbital, unusually, takes busy Bridge Road (and traffic lights!) 8.2-8.6, but NCN61 soon guides us offroad through the suburbs of East Welwyn where we merge with Arc 12 inner to complete the circle together to Hertford.