I really dont know what to do?

Ive asked questions before about a 2 year old and her brother but now there mum is in hospital having had a serious breakdown and there dad was having them but now he's fed up with them and has dumped them on me. Obviously i don't mind as i love them to bits but i can't tell there mum as she is starting to get better i don't want her to get worse if i tell her so im will to keep them until he wants them back or there mum is out of hospital but my cousin says i should tell social services that he doesn't care and dumps them on me but, don't mean this to sound funny but i don't want social services to put them in care, id much rather keep them. What do you think i should do?