Lots of things to consider here.
Pregnancy is considered a medical condition by the cruise lines. For example, they won't accept passengers in their 24th week by the end of the cruise (NCL) or third trimester at the time of cruising (Princess, Carnival)
Norwegian Sky sails from Seattle every Sunday this Alaska season which is convenient for you. The flexible dining of "Freestyle Cruising" would suit you although, food quality on this line isn't as high as other going to Alaska. Also their supervised children's program starts at age 3 unfortunately.
Carnival and Princess have kids programs for 2 year olds:
Carnival's only ship is Carnival Spirit which has amazing kids facilities, It is sailing between Vancouver and Seward in May which means a flight in one direction. This is a brand new ship, inaugural April 29. It has a pool area with retractable dome roof. Group babysitting at night in the kids area but no incabin babysitting on Carnival.
Princess has a kids program for 2 year olds. Their new ships Sun, Sea Dawn and Ocean Princesses, all sail between Vancouver and Seward however, again, a flight needed in one direction. They have the new flexible dining program in effect for Alaska which would be really handy with your 2 year old. They don't have a retractable dome over the swimming pool. In cabin babysitting in the evening.
The older Regal Princess sails the Inside Passage de Passage round trip from Vancouver from May 13. She is looking very elegant after the refit last year. There is a new children's entertainment area on board but it isn't as elaborate as on the other ships mentioned. The bistro on board has 24 hour dining and is very elegant in the evening for candlelight dining as an alternative to the dining room. This ship is very closed in. Outdoor deck space is mainly aft (none forward) so choose your cabin carefully. A mini suite aft, easily accessible to the aft deck space, the bistro and kids center (above the bistro) would be a good choice for you. Incabin babysitting in the evening.
No enclosed pool areas.
Hope that helps answer some of your questions.