Trailer bikes and kids

[winny]

has anyone got experience of these. We have 5 year old on a rack mounted trailer bike which is as solid as a rock and brilliant. 3 year old is too big for rear seat now and so we bought a seat post mounted one but it does seem to wobble and it twists around the post leaving the bike at an angle. I have followed all the instructions and think it is all correct. Has any one else come accross this or am I odd?
I have to sort it before holidays as we are off biking again.
Sorry I posted in family too but couldnt find leisure section

[dot.hawkes]

what is it? can you show us a picture i have no idea what u mean.

[winny]

http://www.spoke.co.uk/cycle_trailers.htm
This is the rack mounted one and this is the post one
http://www.cyclexpress.co.uk/products/Folding_ TrailABike_Single_Speed__Graphite_Grey.aspx

[winny]

Sorry dot the rack one is the red one right at the bottom of the link page