I have 3 children and I will not say it isnt hard because some days it is! I think its mainly because my 2 youngest are s close in age and they fight fight fight!! Shes 5 and hes 6. Those two can be the best of friends one minute and the worst of enemies the next LOL Then I have my daughter who will be 12 this month and shes great (not saying the 2 little ones arent LOL) shes older and we have a great relationship. I guess what Im saying is that You will be fine with 3! oh and this is gonna sound CRAZY but I have looked at this chart and its 100% right with all my kids, my friend has tried it and my cousin as well and it worked LOL just take a look at it
http://www.thelaboroflove.com/chart/cal.html