My son is underweight can cps take him off his dad as im an epileptic (mum)?

i was at a case planning meeting with my ex partner who is a very good dad to both my twin boys and they love him to pieces!! ive not seen them from feb 11 but i was horrified to find out that one of the boys is only 1st 12Pd's!! and they have only given us 3Wks to get some more weight on him!! they will both be three yrs old in july....what can i do to stop the cps from taking my boys away?? and i suffer badly from epilepsy thats why ive not seen them.........someone please help im really worried about my sons and yes my ex is never away from the g.p's surgery he keeps saying as long as the CHILD is drinking fluids then there is nothing to worry about.................PLEASE HELP A VERY DEPRESSED MOTHER!!!!!!!! godbless