S.T.
Mountains & lakes! We began taking the kids on hikes on mountain trails. kids do much better than you'd expect - the tough part is keeping up with them. On the way down they get tired but it makes for good sleeping at nap or bed time. Kayaking is do-able with kids over 4 or 5. Fishing is great fun too - it's amazing to kids that you can catch something in the afternoon and have it for dinner a few hours later. Horseback riding, ziplines, etc. Since it's still chilly stay in a hotel with an indoor pool - good options no matter what.
My kids are teens now and although they like the city and the beaches for daytrips they really enjoy staying up in the mountains and spending time outside for longer vacations - they always want to go back to the mountains but not so much to the beaches.