WDW doesn't sell 3 day park hoppers so if you're going to WDW for only 3 days you could either buy 3 1 day/1 park tickets, a 4 day hopper and save the extra, a 5 day hopper and save the extra or use at DL, or a 2 night/3 day UPH if you're staying on site.
WDW
1 day/1 park = 54.75 +3.56 tax = 58.31
4 day hopper = 202.00 + 13.13 = 215.13 (advanced purchase)
4 day hopper = 219.00 + 14.24 = 233.24
5 day hopper = 230.00 + 14.95 = 244.95 (advanced purchase)
5 day hopper = 249.00 + 16.19 = 265.19
2 night/3 day UPH = 161.00 + 10.48 = 171.48 (advanced)
2 night/3 day UPH = 176.00 + 11.46 = 187.46
3 1 day/1 park tickets would cost 174.93
DL
1 day/1park = 49.75
2 day park hopper = 99.00
DL hotel or good neighbor 2 day park hopper price 98.00
1 day park hopper = 69.00
So 3 1 day/1 park WDW tickets plus a 2 day DL hopper would cost 273.93. Getting a UPH for WDW plus 2 day DL hopper would be 270.48. So if you're only looking to be at WDW 3 days and DL 2 days if you bought a 5 day hopper advanced purchase for WDW you would save 29.98 per person with 1 park/1 day purchase, and 25.53 with a UPH
Kids tickets are
WDW
1 day/1 park = 43.75 + 2.85 = 46.60
5 day hopper = 184.00 + 11.96 = 195.96 (advanced purchase)
UPH = 141.00 + 9.17 = 150.17
UPH = 129.00 + 8.40 = 137.40 (advance purchase)
3 1 day/1park = 139.80
DL
1 day/1 park = 39.75
2 day hopper = 79.00
1 day hopper = 59.00
So 3 1 day/1 park tickets for WDW plus a 2 day hopper for DL would be 218.80, so a savings of 22.84 per child ticket. or advance purchase UPH plus 2 park DL for 216.40, so a savings of 20.44.
In this case if you're not planning on going back to WDW you would save money buying a WDW park hopper and using it at DL. WDW tickets do not expire, DL tickets do, so make sure you don't buy more DL tickets that you need.