I don't have children but I do have vast numbers of children to buy for ( I am starting to sympathise with Carrie in SATC when she realises how much money she has spent on other peoples weddings and children over the years
). some are adorable, others are so scary I won't be left alone with them and I am sure the latter would enjoy:
As an alternative to Sea Monkeys, "Grow your own orcs" kit (complete with slime).
Radio- controlled mumakil (guaranteed to trash the house and complete with real arrow firing action and very sharp tusks).
"Shadowfax" rocking horse - will throw off anyone who tries to ride it (except Gandalf).
Flying balrog - fix to ceiling and watch out for the whip....