A Hampshire Dow is a good fast growing terminal sire ideal to use for fat lambs
However they do have wide heads, wide shoulders and big wide bones in the head, shiulder and legs, taking into account that muscle gives and bone doesn't, I would not put a Hampshire down onto ewe lambs for a first time lambing.
A ewe lambs pelvis is narrow and is not stretched as well as being not fully grown yet, so to breed a ewe lamb for the first time I would always put something with a narrow head, narrow shoulders and fine bones
There may be people out there who have used a Hampshire down on ewe lambs, however I would not do it as if it goes wrong well then you have lost the ewe lamb!
This year I have maybe 20 ewe lambs to go to the tup, but they are all going to the charmoise tup for easy lambing lambs with a low birthweight but high vigour, and then these lambs fill out later on to produce a good carcasses shape
I know someone who puts the charollais ewe lambs to a Shetland with good results, and these ewe lambs are well grown, maybe 50 kilo at time of lambing
Good luck