Labs are great companion dogs and one can keep them in an apartment, but I would not advise you, because.....they are a medium size dog which needs a lot of exercise otherwise they can be quite restless and may get destructive like other breeds also. Your kids are quite big now and can go play in the park with the lab and give it exercise, but again since you have 2 kids in the house, it must be quite a lot of work so I would not advise a medium size dog. Plus labs are kind of continous shedders that is there coat/ hair falls throughout the year. They have these nice tails which wag most of the time and can send things on the table flying since you live in an apartment. They are greedy dogs and at times can eat just about anything anytime and have a tendency to put on a lot of weight if not exercised and kept on a proper diet.
Spaniels.....if you mean the English Cocker Spaniel, then they are much smaller in size as compared to the lab, hence will eat less, are good with kids and playful. yes they have a longer coat hence like most dogs will need to be brushed twice a week atleast, They have long ears so you have to get its ears cleaned and regularly by the vet say once a month or so to be on the safer side and no water should go into the ear while bathing, that is for all breed dogs. Rest is fine. So I would advise for the english cocker spaniel. There is a american cocker spaniel also, but that needs more grooming, trimming and care, so do not go for that one.
I think you live in Delhi and if so delhi has so many pet grooming parlours and vets too do this service and hence you can perhaps ask one to come home every month and bath and groom your dog.
Cockers you can get from 5 grand to anywhere upto 15 odd grands, average 8 grant. Labs again go from 8 odd grant to 25 off grand. What you need to keep in mind is that see both parents and the pups together, otherwise atleast the mother and the pups together, so you know exactly what the pup will grow upto be. If its a pet then papers are not really required as long as you have seen both parents but its a good idea to get them if possible. All pups look very cute and nice but do not get carried away and do not take the children initially as they will then force you to pick up the pup even if the parents are not nice. Wait search see and only then buy rather buying on impulse the first litter you see. This pup will be with you for the next 12 odd years and be prepared to take good care of it and also look at boarding kennels where you can leave the dog incase you are going on holiday and there is no one in the house to take care of it.
I think I did advise you regarding a beagle earlier also, as they are great with kids and have a short coat, but a very loud bark as compared to their size and will cost anything upto 10 to 20 odd grand. Think of the pup as a long term thing and hence do not cut corners in price if possible. There is always a price a price for a reason and be very careful of frauds etc.
All the best and hope the above was helpful. If there is any more specific questions then ask.