Are you sure Owen is Tom and Louisa's child? I can see T & L on the 1901 census with children Nelson (aged 17), Prudence (15) and Lucy (13), but the only 4 yr-old Owen Amer I can see is listed as the son of Owen and Lydia Amer. (Owen Sr is also a hawker.)
Here's the 1901 census:
RG13/1321/58/28
Uxbridge Rd (Caravan), Rickmansworth, Herts
Thomas Amer Head 56 Stall Proprietor at Fairs b Denham, Bucks
Louisa Amer Wife 56 b Chesham, Bucks
Nelson Amer Son 17 Assists Father b Lower Edmonton, Middx
Prudence Amer Dau 15 b High Barnett, Herts
Lucy V(?) Amer Dau 13 b New Bushey, Herts
Rambler