If you are referring to the Views on Venice apartments, it is way too early to book for next April. The apartment owners want to try to get one-week stays booked before they offer shorter stays. Booking six months out, you should see many options with a 3- night minimum. That is all we have ever done with them.
Another local Venetian company we have used is Venice Red House. I see they will,let you book an apartment for 3 nights next April at this time.
This large apartment is €315 a night in early April:
https://veniceredhouse.com/apartments-in-venice/the-arsenal-large-apartment/
This smaller apartment close tomSan Marco if less expensive, but the kids would have to share a sofa bed in the living room.
https://veniceredhouse.com/apartments-in-venice/garden-apartment/
This is the apartment we had for a month some time back; it is around €250/night in early April.
https://veniceredhouse.com/apartments-in-venice/the-lions-house-apartment-lion-4/
The sleeping quarters are separate from the living room and on two different floors, but the kids would have to share a bed here as well. We loved this apartment and the rooftop terrace. But if they kids need separate twin beds, try Lion’s House 3, in the same building one floor down.
https://veniceredhouse.com/apartments-in-venice/the-lions-house-apartment-lion-3/
This location is very central, right near Rialto Bridge, but on quiet Campo San Lio. I don’t know why I didn’t think of mentioning this company earlier, but it is a good option. Each apartment says ‘“3-night minimum” right on the calendar page.
Prices on all these apartments vary by date and go up markedly in mid-April, so I hope your meds’ spring break is early in the month.