I ended up making £1000 in 4 months by selling mine and babies old clothes and bits around the house on vinted. It's kept us afloat during maternity
In most cases you can't work during maternity leave (except KIT days) or you'll automatically end your maternity leave. Could you look at selling some bits? Could your partner pick up some extra work?
This instagrammer did a good post about all the ways to make or save money while on Mat leave: https://www.instagram.com/p/DBIh3fTqQfx/?img_index=5&igsh=MTludjljbXM4MmZ6aA==