Best bet for a good family holidays, especially when you have very young children is to get the grandparents on board and get a nice big cottage somewhere nice. There are hundreds of cottages in fantastic locations around the uk and when we are thinking of our young ones futures, it is worth thinking about staying as local as possible and not going on a jet plane. You will be amazed at some of the beautiful places you never thought existed in the next county or two.
Many holiday cottages cater for families and have multipul bedrooms with large living areas and usful things such as high chairs and cots (Bring your own stairgate is a top tip). Many also cater for a pet as well which I have found very usful.
Beaches are good because the little ones can run around and get rid of all that energy.
Love it local!

Def agree, with under 5's cottages are the way to go. You get all the convenience of home comforts without too much stressful travel. To make it seem more of an adventure for my little ones we went to the Isle of Wight so they got to experience ferry travel. Alot of the tourist attractions were outdated and not relevant to our sons age groups but paddling was always a winner as well as a brilliant little farm where we spent the day. Agree also with last post that flying for holidays is not good for the future of the planet and therefore our children's future.