DD has vague memories of a book she loved as a child but I can't remember it at all. She says:
There was a young girl (maybe 8 or 9) who woke on her birthday to find presents in the living room. She didn't live with her parents, Dd can't remember why. She played for ages with the gifts without opening them, pretending what the contents might be.
It turns out that one of the presents is a machine of some sort that 'makes different things', she makes a huge mess and ends up with three aliens in a pushchair (!).
The person who gave her the gift comes back and tells her how to reverse it so that everything is ok.
Apparently the book was part of a set or series by the same author, one of the others was about a dragon that took people on adventures and another was about travelling on a boat to an island made of edible stuff, with stepping stones across a treacle river, searching for an older relative's secret recipe..
DD says the books were white, soft cover, about the same height as a4 but a bit wider...