A few weeks ago I found one single fry - a guppy and never saw any more and the mother fish died. 
Yesterday I was cleaning the gravel in the tank and two teeny weeny eyes peered up at me so I stopped cleaning gravel and investigated further with help of my 10 year old we spotted 2 more guppy fry (smaller so more recently born I presume) and also 2 platy fry - they are bright orange. Managed to catch them and have them in the 'nursery' tank but today I have spotted another two guppy fry in there sitting hiding behind bits of gravel. I didnt realise any platies were pregnant and my two guppies seem to still be very pregnant.
Is it normal? I thought they kinda gave birth to whole lot at one time rather than still being pregnant but a few are born.

Yesterday I was cleaning the gravel in the tank and two teeny weeny eyes peered up at me so I stopped cleaning gravel and investigated further with help of my 10 year old we spotted 2 more guppy fry (smaller so more recently born I presume) and also 2 platy fry - they are bright orange. Managed to catch them and have them in the 'nursery' tank but today I have spotted another two guppy fry in there sitting hiding behind bits of gravel. I didnt realise any platies were pregnant and my two guppies seem to still be very pregnant.
Is it normal? I thought they kinda gave birth to whole lot at one time rather than still being pregnant but a few are born.